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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
J Fam Psychol. Author manuscript; available in PMC Oct 1, 2010.
Published in final edited form as:
PMCID: PMC2791691
NIHMSID: NIHMS152846

Predictors of Depressive Symptom Trajectories in Mothers of Infants Born Preterm or Low Birthweight

Abstract

Predictors of maternal depression trajectories were examined longitudinally in families with an infant born preterm or low birthweight. A total of 181 mother-infant dyads enrolled in the study prior to the infant’s NICU discharge. Maternal depressive symptoms were assessed at five timepoints, and contextual variables and infant risks were assessed at NICU discharge. Hierarchical linear models revealed that mothers who experienced more risk factors reported more depressive symptoms just prior to their infant’s NICU discharge and showed less decline in depressive symptoms in the months immediately following the child’s birth. Although cumulative risks predicted depression trajectories, this effect appeared driven by maternal and family sociodemographic risks rather than infant risks. Addition of family support as a covariate in the multilevel models with a subsample of families revealed that social support and depression covaried across time. However, most of the findings regarding the association between risk and depression remained consistent, whereas the effects of maternal race and multiple birth were slightly attenuated.

Keywords: cumulative risks, family support, low birthweight, maternal depression, preterm

The number of infants born preterm (< 37 weeks gestation) or low birthweight (< 2500 grams) has increased in the U.S. and other developed countries and more infants are surviving their Neonatal Intensive Care Unit (NICU) stays (Hamilton, Martin, & Ventura, 2007), resulting in a growing number of families facing the challenge of caring for vulnerable infants. Mothers of infants born preterm or low birthweight (PT LBW) are at risk for experiencing psychological distress and depression following the child’s birth, and although these symptoms tend to decrease over time, some mothers remained depressed (e.g., Miles, Holditch-Davis, Schwartz, & Scher, 2007). Because research with fullterms has found links between persistent maternal depression and less optimal child outcomes (e.g., Campbell, Matestic, von Stauffenberg, Mohan & Kirchner, 2007), it is essential to examine predictors of maternal depression trajectories over time in families with PT LBW infants. In addition, because family support has been associated with maternal mental health as well as child outcomes (Malik et al., 2007; Smith & Howard, 2008), examination of this factor in relation to maternal symptom trajectories is important. Such inquiry may provide information about risks for persistent depression in mothers to aid in identifying infants and families most in need of intervention and support while infants are still young. Thus, the goal of the present study was to examine contextual risk variables as predictors of depressive symptom trajectories in mothers of infants born PT LBW during the child’s first two years of life and to determine whether these effects occurred through family support.

Maternal Depression

National prevalence estimates of elevated postpartum depressive symptoms range from 10–30% (e.g, Hiscock & Wake, 2001; Mayberry, Horowitz, & Declercq, 2007; Morris-Rush, Freda, & Bernstein, 2003). Although few studies have followed women past one year postpartum, Mayberry et al. (2007) conducted an analysis of maternal depressive symptoms at two years postpartum in a large, nationally representative sample of mothers. Moderate-to-severe depressive symptoms occurred in 17–24% of mothers in the four cohorts studied, and an additional 11–15% of mothers reported mild depression at two years postpartum, although these rates may be higher for mothers of PT LBW infants. Research with low risk full-terms has documented associations between maternal depression and adverse child outcomes (Murray, Fiori-Cowley & Hooper, 1996), including less optimal cognitive functioning (Hay et al., 2001), parent-infant interaction difficulties (Hart, Field, del Valle & Pelaez-Nogueras, 1998), and behavior problems (Cummings & Davies, 1994). Because outcomes are influenced by the chronicity of depressive symptoms (e.g., Cornish et al., 2005), it is important to consider maternal depression trajectories longitudinally. This is particularly needed in samples of PT LBW infants because they appear more vulnerable to the effects of maternal depression compared to full-terms (e.g., Bugental, Beaulieu, & Schwartz, 2008). For example, Poehlmann and Fiese (2001) found that subclinical maternal depressive symptoms were associated with insecure infant-mother attachment relationships for preterm but not full-term infants.

Preterm Infants and Maternal Depression

The birth of a preterm infant is a nonnormative family transition that can create significant stress as parents attempt to cope with a disrupted or difficulty pregnancy, violated expectations for a healthy infant, fears for the infant’s survival, changes in parenting roles, separation from and lack of physical contact with newborns, intrusive medical interventions (e.g., mechanical ventilation, surgery), and additional medical complications (Davis, Edwards, Mohay, & Wollin, 2003). These stressors and experiences in the NICU setting can contribute to feelings of distress, especially in mothers (e.g., Davis et al., 2003). Indeed, research has documented postnatal elevations in maternal distress in mothers of high risk infants compared to mothers of low risk full-terms (e.g., O’Brien, Asay & McCluskey-Fawcett, 1999; Singer et al., 1999; Younger, Kendell, & Pickler, 1997). In Klebanov and colleagues’ (2001) analysis of IHDP data, mothers of high risk infants who were sicker at birth reported more emotional distress than mothers of infants who were healthier at birth. In addition, Bennet and Slade (1991) found that mothers of higher risk infants reported more emotional distress, more concerns about themselves and their babies, and more difficulty expressing affection towards their newborns than mothers of lower risk infants.

Several studies have assessed maternal depressive symptoms over time in samples of PT LBW infants. In O’Brien et al.’s (1999) study of 45 preterm infants, nearly half of the mothers reported elevated depressive symptoms at three timepoints: during the child’s hospital stay, immediately following hospital discharge, and six weeks after discharge. Depression scores were significantly higher during the infant’s hospitalization than at either of the postdischarge timepoints. Brooten et al. (1988) found that symptoms of depression and anxiety in 47 mothers of high risk preterms decreased between hospital discharge and 9 months. In Mew et al.’s (2003) study of 39 mothers of preterms, 49% of mothers reported elevated depressive symptoms at the child’s hospital discharge, although this decreased to 20% when children reached 6 months.

Two studies focusing on depression in mothers of PT LBW infants have followed families beyond the child’s first year of life. Singer and colleagues (1999) found that mothers of very low birthweight (VLBW) infants reported more distress than mothers of full-terms when infants were one month old. Although mothers of VLBW infants with bronchopulmonary dysplasia (BPD) reported more psychological distress at two years compared to mothers of VLBW infants without BPD and mothers of full-terms, at three years there were no differences in maternal distress symptoms among groups. Miles et al. (2007) assessed maternal depressive symptoms at eight timepoints between birth and 27 months of age in a sample of 102 preterm infants. Their descriptive results indicated that 63% of mothers scored in the clinical range on a depressive symptom questionnaire when infants were still in the hospital. However, average symptoms declined until six months when they became fairly stable, although this pattern varied on the basis of maternal and child characteristics.

It is also important to note that the factors associated with maternal depression are also associated with risk for infant prematurity. Several studies have reported increased risk for preterm labor or lower infant birthwieghts when mothers experience prenatal depression (e.g., Li, Lui, & Odouli, 2009), less social support (e.g., Elsenbruch et al., 2007), or more sociodemographic risks (Luo et al., 2006; Menon, 2008). Although much of the research has focused on maternal depressive symptoms following the birth of a PT LBW infant, it is also possible that symptoms were present during or prior to pregnancy.

Predictors of Maternal Depression

It is imperative to examine predictors of maternal depression trajectories to identify mothers and children most in need of preventive interventions before maternal depression becomes chronic. Several studies have found links between sociodemographic characteristics and rates of depression in mothers, although only one study has examined predictors of depression trajectories in families with preterms. In general, this research has yielded mixed findings. In their representative sample of U.S. mothers, Mayberry et al. (2007) found that younger mothers and women with low incomes, lower education, and more children were more likely to report significant depressive symptoms two years after birth. In Malik et al.’s (2007) study of low income families in Early Head Start, however, maternal socioeconomic variables were only indirectly associated with maternal depression. Similarly, in their study of families with preterm infants, Brooten et al. (1988) found that maternal depression scores at two timepoints did not differ on the basis of marital status, maternal education, or maternal age. Campbell et al. (2007) found that maternal demographic variables such as marital status, race, education, and income were associated with maternal depression trajectories measured annually for seven years in the NICHD early childcare sample of healthy fullterm infants. In contrast, Ashman, Dawson, and Panagiotides’ (2008) study of depressed mothers revealed no association between sociodemographic variables and maternal depression trajectories across five timepoints between infancy and 6.5 years. However, children with prenatal and birth complications were excluded from the study. In Miles et al.’s (2007) study of preterms, unmarried mothers reported more depressive symptoms over time, although maternal education, age, and ethnicity were unrelated to depression trajectories. In addition to marital status, Miles et al. also found that more maternal stress during hospitalization and worry about the infant’s health and development significantly related to maternal depressive symptoms over time, although potential protective processes such as social support were not examined. Although these findings are intriguing, additional research is needed to examine predictors of maternal depression in larger samples of PT LBW infants.

In families with PT LBW infants, infant factors also may relate to maternal depression, including infant birthweight and gestational age, multiple birth, and medical interventions (e.g., ventilation). Mew et al. (2003) found that mothers whose infants required more days of ventilation experienced less decrease in depressive symptoms between the infants’ hospitalization and six months. Using a mixed modeling approach, Miles et al. (2007) found that mothers of infants who were rehospitalized were more likely to experience elevated depressive symptoms during the child’s first two years. Moreover, several studies have documented higher rates of distress and depression in mothers of multiples versus singletons (Bryan, 2003; Garel, Salobir, & Blondel, 1997; Sheard, Cox, Oates, Ndukwe & Glazebrook, 2007; Thorpe, Golding, Mac Gillivray, & Greenwood, 1991). For example, Sheard and colleagues (2007) interviewed 175 mothers who had used in vitro fertilization to conceive. The mothers of multiples were three times more likely to present with clinical indicators of depression when compared to mothers of singletons. However, despite higher prematurity rates and lower birthweights in the multiples group, Sheard et al. did not control for these risks in their analyses, making it difficult to disentangle the effects of multiple birth from the effects of prematurity and other neonatal risks.

Family Support

Family support has the potential to play a crucial role in how maternal depression trajectories unfold over time (e.g., Smith & Howard, 2008) and for children’s outcomes (Dawson et al., 2003; Malik et al., 2007), particularly in families of preterm infants (Logsdon & Usui, 2001). Research has found that more perceived emotional and instrumental support is associated with less maternal depression, although the relations between support and depression may vary with child age, type of support, and the accumulation of stressors. For example, in their study of families of healthy full-terms, Smith and Howard (2008) reported that partner-provided support and maternal depression trajectories varied with infant age. Shortly after birth, partner support decreased as maternal depression decreased. In contrast, when infants were 24 months of age, less support was associated with more maternal depression. For families facing multiple stressors, lack of emotional support may be another risk for depression (e.g., Zunzunegui, LlacerCentro & Beland, 2002); conversely, high levels of social support may buffer the negative effects of poverty (e.g., Shultz et al., 2006) and other risks.

For mothers of infants born preterm, studies have shown benefits from formal support services (e.g., Infant Health and Development Program, 1990) and from support provided by partners (Lee, Holdtich-Davis, & Miles, 2007), extended family (e.g., Rempusheski, 1990), and medical staff (Davis et al., 2003). For families raising preterm infants, the roles of emotional and instrumental support from family members may be particularly salient, given the elevated rates of distress reported by mothers.

Theoretical Perspectives

Ecological theory posits that multiple levels of contextual influence affect individual development over time (Bronfenbrenner, 1986). Proximal processes, such as those that occur in a person’s immediate context, are thought to be most influential for development and are likely to mediate the effects of more distal factors (Bronfenbrenner & Ceci, 1994). For a mother who is coping with the birth of a PT LBW infant, proximal processes may be reflected in the infant’s health status as well as individual sociodemographic factors (e.g., age, education). In addition, provision of support from family members may be an important proximal process that may function in a protective capacity (Malik et al., 2007; Smith & Howard, 2008). More distal factors such as family income or stress associated with racial disparities may also play a role in how these mothers cope. For example, Linver, Brooks-Gunn, and Kohen’s (2002) analysis of IHDP data showed that family poverty was associated with less optimal parenting and more maternal distress in families with low birthweight infants.

In contrast, transactional developmental theory (Sameroff & Fiese, 2000) posits that the accumulation of environmental risk factors, rather than any particular risk, is a key contributor to developmental and social outcomes. Multiple risks are thought to exert their influence via ongoing transactions between the individual and context over time. Research has found that the experience of more risks is related to less optimal cognitive, behavioral, and health outcomes for children (e.g., Sameroff, Bartko, Baldwin, Baldwin, & Seifer, 1998; Larson, Russ, Crall, & Halfon, 2008; Liaw & Brooks-Gunn, 1994) and more behavior problems and depression for adolescents (e.g., Gerard & Buehler, 2004). On the basis of past research, it is unclear whether particular risk factors, clusters of maternal or infant risks, or accumulated risks are associated with depression trajectories in mothers of PT LBW infants. Addressing this question can inform screening efforts and the design of preventive interventions for medically fragile infants that seek to increase resilience processes, or successful adaptation in children who experience significant adversity (e.g., Masten, 2001).

Because the rate of preterm birth is higher for Black and Latina women than White women (e.g., Reagan & Salsberry, 2005) and economic disparities are present for many members of underrepresented groups (e.g., Harrison-Hale, McLoyd, & Smedley, 2004), maternal race is also a potentially important consideration. Moreover, prevalence rates suggest that postpartum depression is more common in African American and Hispanic women compared to Caucasian women (Howell, Mora, Horowitz, & Leventhal, 2005). Because of these factors, we included maternal race as a control variable in our analyses.

Research Questions and Hypotheses

The primary goal of the study was to compare three risk models to predict maternal depressive symptoms at NICU discharge and maternal depression trajectories across PT LBW infants’ first two years of life. In the first model, we included specific ecological variables as predictors. In the second model, we examined cumulative risks as predictors of maternal depression intercept and trajectories, and in the final model, we included maternal and infant risks as predictors of maternal depression at NICU discharge and over time. We hypothesized that the cumulative risk model would best predict maternal depression intercept and trajectories. All models controlled for maternal race.

The secondary goal of the study was to examine family support as reported by mothers of PT LBW infants as a covariate of maternal depression to help offer potential explanations for associations identified between risk variables and maternal depression trajectories.

Method

Participants

A total of 181 mothers and their infants were recruited from three NICU’s in southeastern Wisconsin between 2002 and 2005 as part of a larger study focusing on the development of self-regulation in infants born PT LBW (Poehlmann et al., 2009). A research nurse from each hospital invited families to participate in the study if they met the following criteria: (a) infants were born ≤ 35 weeks gestation or weighed less than 2500 grams at birth, (b) infants had no known congenital malformations or prenatal drug exposures, (c) mothers were at least 17 years of age, (c) mothers could read English, and (d) mothers self-identified as the child’s primary caregiver. When mothers had multiples (i.e., twins or triplets), one infant was randomly selected to participate in the study. Because the hospitals would not allow us to be “first contact” for families and they only provided us with information about families who signed consent forms for the study, we were unable to calculate a participation rate. Of the 186 mothers who signed consent forms, 181 (97%) participated in data collection. In addition, participant family characteristics paralleled the population of Wisconsin during the data collection period. For example, 77% of mothers who gave birth in 2005 in Wisconsin were White, 9% were Black, and 9% were Latina (Martin et al., 2007); although the rate of preterm birth was generally higher for Black (18.4%) than White (11.7%) infants (Hamilton et al., 2007). In our sample, 66% of the infants that we enrolled in the study were White, 14% were Black, 2% were Hispanic/Latino, and 17% were multiracial (most multiracial infants were Black and either White or Hispanic/Latino). In Wisconsin, 89% of mothers who gave birth were between 20 and 39 years of age, and an average of 15.5% of children lived in poverty in Wisconsin between 2003 and 2005 (US Bureau of Census, 2003–2005). Approximately 86% of the mothers in our sample were between 20 and 39 years of age at the time of hospital discharge, and 31 (17%) were living in poverty. See Table 1 for additional sample characteristics.

Table 1
Demographic and Neonatal Characteristics at NICU Discharge (n = 181)

Infants and their families were assessed at five time points: just prior to the infant’s hospital discharge and again at 4, 9, 16, and 24 months corrected age. Corrected age was calculated on the basis of the infant’s due date and is commonly used for assessments of preterm infants’ development (DiPietro & Allen, 1991). There was a 14% attrition rate between NICU discharge and 24 months. Multivariate analysis of variance (MANOVA) was used to examine potential differences between families who continued in the study for two years and families lost to attrition. The first MANOVA was conducted on infant health variables and revealed no significant differences (multivariate F(6,172) = 1.36, p = .24) for infant gestational age, birthweight, 1- and 5-minute Apgar scores, days hospitalized, or the neonatal health risk index. The second MANOVA, conducted on Time 1 family sociodemographic variables, approached trend level significance (multivariate F(7,167) = 1.90, p < .08). Follow-up univariate tests indicated that mothers who were lost to attrition were younger (F(1,173) = 5.51, p < .05), had completed fewer years of education (F(1,173) = 5.88, p < .05), and had slightly higher sociodemographic risk index scores (F(1,173) = 3.23, p < .08). However, the groups did not differ on number of children in the family, the father’s age or education, or family income. Chi-square analyses revealed that mothers lost to attrition also were more likely to be single (χ2(1) = 4.68, p < .05) and nonwhite (χ2(1) = 5.57, p < .05). However, attrition did not differ for families who had multiples or singletons, χ2(1) = 1.46, p = .23, or on the basis of parental employment status, χ2(1) = 0.33, p = .57. A one-way ANOVA revealed that Time 1 depressive symptoms did not significantly differ between mothers who continued in the study and mothers lost to attrition by 24 months (F(1,177) = 0.35, p = 56.). In addition, there were no differences in families with and without multiple births regarding maternal or paternal age, maternal or paternal education, family income (multivariate F (5,143) = 1.04, p = .39), or marital status (χ2(1) = 2.22, p = .14. There were also no differences in birthweight, gestational age, or days hospitalized for multiples and singletons, multivariate F (3,177) = 0.28, p = .84.

Our attrition rate is similar to or less than other longitudinal studies of high risk infants. For example, Miles et al. (2007) had 27% attrition across 27 months in their longitudinal study of VLBW infants. In addition, although the Infant Health and Development program had a 7% attrition rate during 3 years of the intervention program that did not differ by treatment group, 28.5% of their sample had missing data, and mothers of children with missing data were significantly younger, less educated, and nonwhite (e.g., Liaw & Brooks-Gunn, 1994).

Infant birthweights ranged from 490g to 3328g, with a mean of 1713g (SD = 589g). Infant gestational age ranged from 23 to 37 weeks, with a mean of 31.4 weeks (SD = 3.15), and infants spent an average of 33 days (SD = 28.01) in the NICU. Thirty-four (19%) of the infants were part of a multiple birth (i.e., twins, triplets). At hospital discharge, mothers were an average of 29 years old (SD = 6.24) and had obtained 14 years of education (SD = 2.70). Most mothers (n = 125, 70%) reported that they were married, and the average household income at hospital discharge was $59,995 (SD = $53,563). Ninety-six (53%) infants were boys and 85 (47%) infants were girls.

Measures

Maternal and Family Sociodemographic Assets and Risks

Mothers completed a demographic questionnaire while their infants were in the NICU. Data were collected regarding maternal age and years of education, family income, number of dependents in the home, and parental marital status (coded 1 = parents married, 0 = not married), and maternal race (1 = white, 0 = nonwhite). This information was used to generate two indices: an index of maternal assets used in the “individual variables” model and an index of maternal sociodemographic risks used in the “cumulative risk” and “maternal and infant risk” models.

For the maternal assets index, maternal age, education, and family income were standardized and summed because these variables were highly correlated (r’s = .51, p < .001). Cronbach’s α for the composite was .76.

To generate a maternal and family sociodemographic risk index, one point was given for each of the following risks on the basis of previous research (e.g, Sameroff et al., 1998): the family’s income was below the federal poverty guidelines adjusted for family size, the mother was single, the mother had given birth as a teen, the family had four or more dependent children in the home, and the mother had less than a high school education. Families could receive a risk score ranging from 0 to 5, with higher scores reflecting more sociodemographic risks. Cronbach’s α for the sociodemographic index was .70.

Infant Risks

Medical records were reviewed following infants’ NICU discharge. We coded this information in two ways: (1) by creating a prematurity composite for use in the “individual variables” model, and (2) by creating an infant risk index for use in the “cumulative risk” and “maternal and infant risk” models.

Because infant birthweight and gestational age were highly correlated (r = .88, p < .001), we standardized and summed them to generate an infant prematurity composite. The composite ranged from −4.39 to 3.90 with an average of .12 (SD = 1.98), with higher scores representing less prematurity. We also coded whether the infant experienced ventilation (CPAP or mechanical), whether the infant was part of a multiple birth, and the length of the NICU stay.

To create an infant risk index, one point was given for each of the following risks: the child experienced ventilation, the child was born less than 1000 grams, the child was part of a multiple birth, and the child spent more than 30 days in the hospital. Each infant received a risk score ranging from 0 to 4, with higher scores representing more risks. Cronbach’s α was .54.

Cumulative Risks

The sociodemographic and infant risk indices were summed to create a cumulative risk index (to be used in the “cumulative risk” model). The index could range from 0 to 9, with higher scores representing more risks. Cronbach’s α was .62 for the index.

Maternal Depressive Symptoms

The Center for Epidemiologic Studies-Depression Scale (Radloff, 1977; CES-D) was used to assess maternal depressive symptoms at each timepoint via maternal self-report. The CES-D is a 20 item questionnaire that asks respondents to rate their symptoms on a 4 point scale ranging from rarely/none of the time (0) to most/all of the time (3) during the past week. Scores of 16 and above are considered in the clinical range. The CES-D discriminates between patients and nonpatients and has been used extensively in clinical and epidemiological research, including research with mothers of young children (e.g., Lyons-Ruth, Zoll, Connell, & Grunebaum, 1986). Alphas for the present study were .87, .85, .88, .87, and .89 for the NICU discharge and 4, 9, 16, and 24 months timepoints, respectively. At NICU discharge, 32% of mothers reported symptoms in the clinically significant range, whereas this decreased to 19% at 4 months, 17% at 9 months, 11% at 16 months, and 12% at 24 months.

Family Support

Maternal report of family support at each timepoint was assessed using the Maternal Support Scale (MSS; author citation, unpublished document). The MSS is a self-report measure that inquires about support received by mothers from the child’s father and the mother’s parents, in-laws, and extended family. Mothers rate whether or not support was received from each source across seven areas: emotional, information, household, childcare, financial, rest, and other support. A total Family Support scale was created for each timepoint by summing these seven items across the four sources of support, resulting in scores that could range from 0 to 28, with higher scores reflecting receipt of more family support. Alphas for the Family Support scale ranged from .83 to .86 across timepoints.

The support measure was available at hospital discharge for a subsample of 157 (87%) families because it was added to the larger study as part of a later supplemental protocol. These 157 families were comparable to the first 25 families who did not complete the form on mean CESD scores, maternal and family demographic risks, neonatal risks, and attrition rate.

Procedure

Families were enrolled in the study through three hospitals in southeastern Wisconsin, following Institutional Review Board approval from the University of Wisconsin and each of the hospitals. An IRB approved brochure was distributed to families in each NICU, and a research nurse from each hospital described the study to eligible families by verbally summarizing and giving them a copy of the consent form. Interested mothers returned the signed informed consent forms to nurses who alerted researchers when the infant was close to discharge. A researcher met the mother at the NICU just prior to the infant’s discharge to collect Time 1 data, and mothers completed self-administered questionnaires including a demographic form and the CESD at that time. Each mother was given a list of clinics and agencies that could assist her if she felt distressed. In addition, if a mother reported clinically significant depressive symptoms at any timepoint, the study PI (a licensed psychologist) called the mother to offer follow-up and referral information. Nurses completed a history of hospitalization form by reviewing the infant’s medical records shortly after NICU discharge. Home visits were conducted with families when infants were 4 and 9 months corrected age. At these visits, researchers asked mothers to complete self-administered questionnaires in addition to videotaping mother-child interactions. Each of the home visits lasted approximately 1.5 hours. Mothers were paid $25 for the 4 month visit and $40 for the 9 month visit. When infants were 16 and 24 months postterm, families visited our laboratory playroom. Mothers and children were videotaped playing together and mothers completed self-administered questionnaires while a researcher administered a standardized developmental assessment to the child. Each of the laboratory visits lasted approximately 1.5 to 2 hours. Mothers were paid $65 at the 16 month visit and $80 at the 24 month visit. Children were given an age-appropriate book or toy at the end of each visit.

Plan of Analysis

To address our research questions, we used multilevel modeling procedures. Multilevel model analyses, also known as hierarchical linear models (HLM), random coefficients models, or mixed models (Raudenbush & Bryk, 2002), are increasingly used in developmental and family research. Using this approach, repeated measures are seen as nested within individuals. There are several advantages to using multilevel analyses. By treating independent variables as random effects, multilevel approaches can simultaneously estimate growth curves or unique regression equations for individuals. In addition, variance and covariance parameters can be estimated for regression parameters such as the intercept or slope. The covariance between the model intercept and the model slope also can be examined. In the present study, we focused on early contextual predictors of maternal depression intercept and slope.

To address our secondary research question, we conducted a second set of multilevel models with family support covarying with depressive symptoms across time.

Results

Variables were screened for outliers, distributions, and for other statistical assumptions (Raudenbush & Bryk, 2002). No transformations or removal of outliers was necessary.

We used two-level hierarchical linear models to predict individual change in maternal depressive symptoms over time (Raudenbush & Bryk 2002; Raudenbush, Bryk, & Congdon, 2005). The level 1 model specified the shape of individual change trajectories with respect to individual parameters (i.e., intercept, linear growth rate, and acceleration). The level 2 models assumed that growth parameters varied among individuals. These models tested the effects of early maternal and infant risks on the individual change parameters while controlling for the effects of maternal race. Full maximum likelihood estimates were used in all models, represented by the following equations:

Level 1 model

CESD=P0+P1(MONTHS)+P2(MONTHS2)+e

Level 2 model

P0=B00+B01(RISK)+B02(RACE)+R0P1=B10+B11(RISK)+B12(RACE)+R1P2=B20+B21(RISK)+B22(RACE)+R2

For each theoretically-driven model examined, both linear and quadratic models were fitted. Because we were interested in the possibility of early screening, we set Months to 0 as the NICU data collection point so the intercept represented depressive symptoms at this timepoint.

Unconditional Model

We examined linear and quadratic unconditional models to determine the nature of the model that best described trajectories of maternal depressive symptoms and to quantify variance in trajectory parameters across mothers. On the basis of deviance statistics, the quadratic model provided a statistically superior fit to the linear model (χ2 (5) =51.69, p < .001). For this reason, we will focus our interpretation on the quadratic model results. Because race was coded 0 = white, 1 = nonwhite, the baseline condition reflects the expected trajectory for a white mother. Thus for white mothers, there were significant fixed effects for both the linear and quadratic terms, indicating that the trajectory of maternal depressive symptoms had, on average, a decreasing trend (following a somewhat elevated initial level), and one that became progressively less decreasing over time. The only statistically detectable effect of race was found with respect to the intercept, implying higher depression scores for nonwhite mothers just prior to NICU discharge. Deviance testing also confirmed statistically significant variability in linear and quadratic terms across mothers for the quadratic model (χ2 (5) =35.32, p < .001), suggesting variability in the trajectories that may be explained by level-2 predictors.

Assessment of Risk Models

Individual Variables Model

In this model, we entered the individual maternal and infant variables as predictors of maternal depression slope and intercept. The maternal variables included marital status, number of children in the home, and the maternal assets index. Infant variables included the prematurity composite, number of days in the NICU, use of ventilation, and multiple birth. Table 2 shows the fixed effects and deviance scores for the individual variables model for both the linear and quadratic models and the residual variance of each of the trajectory parameters. In the linear model, we found that none of the individual variables significantly predicted maternal depression intercept or slope. In the quadratic model, however, multiple birth was a significant predictor of maternal depression scores just prior to NICU discharge, with mothers who gave birth to multiples reporting fewer symptoms. In addition, the quadratic slope was predicted by the intercept, the maternal assets index, multiple birth, and maternal race. It can be easier to interpret these effects graphically, as it is difficult to offer clear interpretations of the separate effects on individual parameters in a quadratic model. Figure 1 displays the model-based average trajectories for mothers at different levels of predictors found significant. In each panel, the curves reflect the effects of a different predictor. Each trajectory was plotted according to the specified level of the relevant predictor while assigning all other predictors to either their baseline (nonmarried, white, singleton birth, no ventilation) or mean (number of children, days in NICU, infant prematurity composite, maternal assets) levels. As the maternal asset index is continuous, the trajectories shown in the first panel are considered at three different levels: the maternal assets mean and ±1 standard deviation.

Figure 1
Average Quadratic Trajectories as Defined by Significant Predictors: Individual Model.
Table 2
Linear and Quadratic Individual Variables Model Estimates (n = 179)

For each variable found significant in prediction of the trajectory parameters, the effects of predictors can be interpreted with respect to the nature of change in depression scores seen in the months following birth. Mothers with varying levels of maternal assets (age, education, income) had approximately the same level of depression following birth, although a steeper decline in depression was seen for mothers with more maternal assets in the months immediately following birth, before returning to a common level at 20+ months. In contrast, mothers of multiples had initially lower levels of depression following birth but slower rates of decline over time in comparison to mothers of singletons. Finally, the effects of race appeared to be largely the same as observed in the unconditional model, although differences in the quadratic terms emerged as statistically significant in this model. Nonwhite mothers reported initially higher symptoms, with a steeper decrease in symptoms until reaching a similar level as white mothers at about 9–16 months, when their symptom level increased slightly through 24 months.

Cumulative Risk Model

To examine the accumulation of risks as a predictor of maternal depression slope and intercept, the effect of the cumulative risk index was estimated (Table 3). In the linear model, the cumulative risk index was significantly related to the slope but not the intercept. On average, depressive symptoms for mothers who experienced more cumulative risks displayed a lesser decrease over time. In the quadratic model, the cumulative risk factor emerged as a significant predictor of both the linear and quadratic coefficients, but not the intercept, whereas race was significantly related to both the intercept and quadratic coefficients. The effects of these predictors are depicted graphically in Figure 2. Similar to the maternal assets index in the individual model, the effects of cumulative risk are shown with respect to hypothetical mothers at the mean and at ±1 standard deviations on the cumulative risk index. Mothers who experienced high levels of cumulative risk displayed slower rates of decline in depressive symptoms in the initial months following birth, and although their symptoms eventually began to decline, their average level of symptoms remained relatively high. The effects of race appeared largely the same as in the unconditional and individual models.

Figure 2
Average Quadratic Trajectories as Defined by Significant Predictors: Cumulative Risk
Table 3
Linear and Quadratic Cumulative Risk Model Estimates (n = 179)

Maternal and Infant Risk Model

Because it is important to understand whether maternal or infant risks are driving the model, we also entered the infant and maternal risk indices separately in a third model (Table 4). In the linear model, the maternal risk index predicted the intercept and slope. Mothers who experienced more sociodemographic risks had significantly higher Time 1 depression scores and they also showed less decline in symptoms over time. In the quadratic model, none of the variables predicted the intercept. However, the maternal and infant risk indices significantly related to the linear and quadratic coefficients (see Figure 3). Mothers who experienced more sociodemographic risks demonstrated, on average, a slower initial decline in depressive symptoms in the months immediately following birth, an effect similar to that observed for the cumulative risk index. Whereas a similar pattern of change was observed for the infant risk variable, the nature of this variable’s effect on the intercept (although nonsignificant) made the change in trajectory less noticeable, and potentially of less consequence. These patterns suggested that maternal risks appear to be driving the cumulative risk effect. In this model, race displayed a similar effect to that observed in the previous models.

Figure 3
Average Quadratic Trajectories as Defined by Significant Predictors: Demographic and Infant Risks
Table 4
Linear and Quadratic Sociodemographic and Infant Risk Model Estimates (n = 179)

Family Support Analyses

HLM analyses that covaried out the effects of family support were performed for each model assessed above with the subsample of 157 families for which the family support measure was available. This entailed entering total family support as an additional level 1 predictor variable having fixed effects across persons. For example, in the quadratic cumulative risk model, the following model was specified:

Level 1 model

CESD=P0+P1(MONTHS)+P2(MONTHS2)+P3(FAM_SUPPORT)+e

Level 2 model

P0=B00+B01(RISK)+B02(RACE)+R0P1=B10+B11(RISK)+B12(RACE)+R1P2=B20+B21(RISK)+B22(RACE)+R2P3=B30

By entering family support in this way, the effects of our risk variables could be evaluated according to how they influenced depression above and beyond what was explained by family support. Similarly, the trajectory parameters (P0, P1, P2) represented fluctuations in depression as the result of factors other than what was explained by changes in family support. By comparing the variable coefficients from this analysis against those of the analyses without family support included, we were able to evaluate which variables may have exhibited their effectts on depression through family support.

In each model assessed, family support was significantly and negatively associated with depression scores, indicating that within persons, as family support increased (or decreased) over time, depression correspondingly decreased (or increased).

With family support added as a level 1 predictor variable, most of the findings in the risk models remained the same. Only four differences in the patterns of statistical significance emerged across models: (1) in the unconditional model, the effect of race on the depression intercept was reduced to a trend suggesting that a portion of this effect was a function of differences in family support; (2) in the linear individual risk model, maternal assets became a significant predictor of the maternal depression intercept after covarying family support, whereas the effect of multiple birth on the intercept was reduced to a trend; (3) in the quadratic cumulative risk model, the effect of race on the intercept was reduced to a trend and the intercept became a significant predictor of the quadratic slope; and (4) in the maternal and infant risk model, the intercept and maternal race became significant predictors of the linear and quadratic coefficients in addition to the effects of maternal and infant risk. In all cases, the quantification of predictor coefficients remained largely unchanged, with the largest change occurring in the effect of multiple birth, where the intercept coefficient was reduced about 25% in magnitude.

Discussion

In our prospective longitudinal study of families with infants born preterm or low birthweight, we examined early predictors of maternal depressive symptom trajectories across a two-year period. We also examined family support over time as it covaried with depressive symptoms. Our descriptive findings indicated that, on average, maternal depressive symptoms decreased over time from a somewhat elevated initial level, and within persons, as family support increased (or decreased) over time, depression correspondingly decreased (or increased). We found that mothers who experienced an accumulation of maternal, infant, and family risks prior to the infant’s NICU discharge showed less decline in depressive symptoms in the months immediately following the child’s birth, with their symptoms remaining relatively high compared to mothers who experienced few risk factors. Comparison of risk models indicated that this effect was driven by maternal sociodemographic risks somewhat more than infant health risks, although both types of risks significantly contributed to depression trajectories.

These findings highlight the need for screenings in the NICU setting and suggest both “who” and “what” should be targeted. Early screening can help identify who is most at risk, and therefore appropriate referrals and interventions can be directed toward the highest risk groups while infants are still young. The “who” variables identified in this study include mothers of infants who weighed less than 1000 grams, had lengthy NICU stays, and experienced ventilation in the context of maternal sociodemographic risks (e.g., poverty and low education) and low social support. Early screening also benefits infants and families by focusing on specific factors or processes that can be ameliorated through intervention or treatment to increase resilience processes. In the present study, we found that, controlling for family support across time, NICU discharge depression scores significantly predicted elevated depression trajectories in both the cumulative and individual risk models. These findings suggest that screening of maternal depressive symptoms prior to NICU discharge may be useful in identifying mothers at highest risk for developing chronic depression In addition, because receipt of family support related to maternal depressive symptoms in all models assessed, this factor should be considered when determining key components of screening and intervention programs, as we discuss below.

Following the birth of a PT LBW infant, mothers often experience psychological distress and depression (e.g., O’Brien et al., 1999; Singer et al., 1999), in part because of the unexpected and nonnormative nature of the event and possible medical complications and interventions, worry about the child’s survival, and long NICU stays (Davis et al., 2003). In our sample, 32% of mothers reported clinically significant depressive symptoms just prior to the infant’s NICU discharge, whereas this decreased to 12% by 24 months postterm. Although the average pattern reflected decreasing symptoms, with some leveling off between 16 and 24 months postterm, we also found that an accumulation of risks predicted maternal trajectories.

Research guided by transactional developmental theory (Sameroff & Fiese, 2000) has found that cumulative environmental risks relate to less optimal outcomes for children and adolescents (e.g., Gerard & Buehler, 2004; Sameroff et al., 1998; Larson et al., 2008; Liaw & Brooks-Gunn, 1994). However, it is important to identify clusters of risks that may be particularly potent for families. In our sample of PT LBW infants, mothers experiencing more sociodemographic risks reported elevated depressive symptoms just prior to the infant’s NICU discharge and they did not experience the normative decrease in symptoms over time, suggesting the possibility of chronically elevated symptoms. The accumulation of risks such as living in poverty, being a single mother, having four or more children, giving birth as a teen, and having less than a high school education, was associated more vulnerability to the experience of chronic depressive symptoms in the context of having a PT LBW infant. Because previous research has found evidence linking chronic maternal depression with less optimal child outcomes (Campbell et al., 2007; NICHD ECRN, 1999), infants of affected mothers may be at high risk for developing problems over time, particularly in the context of preterm birth. Early identification of the highest risk mothers, infants, and families may allow interventions focused on decreasing maternal distress and supporting child development to be initiated when children are very young.

Our results are consistent with Mayberry et al. (2007), who found that younger mothers and women with lower incomes, less education, and more children were more likely to report significant depressive symptoms when children were two years old in their nationally representative sample. Similarly, Campbell et al. (2007) found that maternal marital status, race, education, and income were associated with maternal depression trajectories across seven years in the NICHD sample of healthy fullterm infants. In two studies focusing on preterms, however, maternal education and age were not associated with maternal symptom levels (Brooten et al, 1988; Miles et al., 2007), although these studies used smaller sample sizes. Miles et al. (2007) found that unmarried mothers of preterms reported more depressive symptoms over time than married mothers, yet they did not find a cumulative risk effect. Although their original sample of 102 mothers was diverse, Miles et al. had a 27% attrition rate between enrollment at 27 months and their sample included only high risk preterms (i.e., preterms who were born at less than 1500 grams or who required mechanical ventilation or continuous positive airway pressure).

The interplay of preterm birth, maternal race and ethnicity, family support, economic disadvantage and maternal psychological well-being is particularly complex because factors in the broader social context, such as racial discrimination and residential segregation, influence mothers’ abilities to receive adequate prenatal care and have healthy pregnancies, thereby increasing risk for preterm birth (e.g., Bell, Zimmerman, Almgren, Mayer, & Huebner, 2006; Reagan & Salsberry, 2005). This broader social context also impacts depressive symptoms among lower income and ethnic minority women more generally (McGrath et al., 1990). Like those women at risk for preterm births, women at risk for elevated depressive symptoms are more likely to experience risks such as housing instability, lower social support, and more social isolation (McLoyd, 1998; Bell, Zimmerman, Almgren, Mayer, & Huebner, 2006).

Our findings suggest that mothers from racial/ethnic minority groups experienced significantly different depression trajectories than their white counterparts; however, when family support was added to the model, these effects were attenuated. Although their symptom level was somewhat higher initially, they experienced a steeper decrease in symptoms so that their average level was similar by 9–16 months postterm. This finding may reflect the highly mobilized informal support networks of African American mothers following the birth of a PT LBW infant (Barton, Roman, Fitzgerald, & McKinney, 2002), although additional research is needed to confirm this speculation. Although the overall nonwhite group was relatively small, the diversity within it suggests that the differences in depression trajectories or family support are not the function of specific racial or ethnic group membership but more a reflection of sociodemographic risk and family support. This premise is supported by our findings that the effects of race were attenuated in some models following the entry of the demographic risk and family support variables. Despite these findings, it is important to recognize that nonwhite mothers may experience elevated rates of postpartum depression (Howell et al., 2005), and racial disparities exist in access to appropriate treatment for depression, particularly for African American and Hispanic mothers compared to Caucasian mothers (e.g., Zittel-Palamara, Rockmaker, Schwabel, Weinstein, & Thompson, 2008). Future research that includes both socioeconomic and racial/ethnic diversity is needed to further delineate the impact of race on depression in mothers of PT LBW infants, including their access to appropriate treatment.

Our finding that increases (or decreases) in social support over time were related to decreases (or increases) in depressive symptoms after a preterm or low birthweight birth is consistent with previous observations of an inverse relationship between social support and depressive symptoms for women during pregnancy (Ritter, Hobfall, Lavin, Cameron, & Hulsizer, 2000). Further, in an analysis of data from 40,333 Australian women between 2002 and 2005, Milgrom and colleagues (2008) determined that lower support and depressive symptoms during pregnancy and lifetime depression history were predictors of postnatal depression. Elsenbruch et al. (2007) made similar observations among 896 pregnant women. They followed these women throughout their pregnancies and after the births of their babies and determined that higher antenatal social support predicted better birth outcomes. Indeed, factors associated with postnatal depression are also associated with risk for infant prematurity. Previous research has found increased risk for preterm labor when mothers experience prenatal depression (e.g., Li, Lui, & Odouli, 2009), less social support (e.g., Elsenbruch et al., 2007), or more sociodemographic risks (Luo et al., 2006; Menon, 2008). Together, these findings indicate that screening and intervention for women would ideally begin as early as possible. These findings further suggest that improving the overall mental health of women, regardless of their current pregnancy status, may be one means of improving children’s birth outcomes and subsequent development. Such interventions are especially important in low income and ethnic minority communities because they experience elevated risk for developing depressive symptoms (McGrath, Keita, Strickland, & Russo, 1990).

After controlling for sociodemographic risk and family support, we found that racial/ethnic minority mothers experienced increased depressive symptoms after an initial steep decline following NICU discharge. Although universal screening of women for depression would be ideal, this finding points to specific demographic groups and timepoints that could be targeted for screening and intervention. In addition to screening for depression, mothers’ receipt of social support could be assessed. Intervention efforts could then focus on strengthening existing family-based or community networks, helping mothers utilize additional resources, or providing a temporary support structure (e.g., Dennis & Kingston, 2008; Preyde, 2007).

Our findings further suggest that screening and intervention should take place in the NICU in anticipation of a vulnerable period of time that appears to occur between 16 and 24 months for racial/ethnic minority and high sociodemographic risk mothers. In an example of such an intervention, Preyde and Ardal (2003) observed that mothers who participated in a NICU-based “buddy” program for mothers of infants born at less than 30 weeks gestation reported less stress, lower depression, and more social support than mothers who did not receive intervention. Although the intervention group was small (n = 32) and the study did not follow participants longitudinally, the findings suggest that this type of programming may be a means of improving mother and child outcomes and promoting resilience processes in vulnerable families.

Although infant health risks did not appear to drive the models that described chronically elevated depressive symptoms, mothers who gave birth to multiples reported fewer depressive symptoms at NICU discharge but then experienced a slower decline in symptoms over time compared to mothers of singletons. Previous research has found elevated rates of depression and stress in mothers of multiples compared to singletons (Bryan, 2003; Sheard, Cox, Oates, Ndukwe, & Glazebrook, 2007). However, because the rates of PT LBW births are high for multiple pregnancies and have increased in recent years (Blondel et al., 2002), mothers of multiples may be more prepared for this experience. They also may receive more support than mothers of singletons following birth. Indeed, when we added family support to our HLM models, we found that the effect of multiple birth was attenuated. Moreover, stressors associated with having a PT LBW infant may be less pronounced prior to discharge from the special care nursery in these families. Over time, however, the strain of caring for multiples (especially triplets, e.g., Feldman & Eidelman, 2004) may cause mothers to experience less decline in their level of depressive symptoms, as previous research has found that mothers of multiples face greater child care needs and more stress than mothers of singletons as time goes by (e.g., Taylor & Emery, 1988–1989). Similarly, in another analysis of our data set, we found that mothers of multiples born PT LBW reported more parenting stress and parenting daily hassles than mothers of PT LBW singletons at 24 months postterm (Lutz & Poehlmann, 2009). However, it should be noted that many other studies examining differences in family reactions to multiples compared to singletons have not controlled for infant prematurity or birthweight (Ellison et al., 2005; Sheard et al., 2007; Sutcliffe & Derom, 2006). This would be an important consideration in future research because caring for even one PT LBW or medically fragile infant can be stressful.

The limitations of this study should be considered when interpreting or applying our findings. Because we focused on infants born PT LBW, our results are not generalizable to low risk full-terms. In addition, although our attrition rate was relatively low across two years for a sample of high risk infants, families who dropped out of the study or could not be located were slightly more socioeconomically disadvantaged than ones remaining in the study. We also relied on self-reports of depressive symptoms rather than depression diagnoses. Because maternal reports on depression screening measures can also reflect more general psychological distress or anxiety (Boyd, Le, & Somberg, 2005; DiPietro, Costigan, & Sipsma, 2008), this should be considered when interpreting our results. Perhaps more importantly, we did not assess pregnancy or prepregnancy depressive symptoms, nor did we assess whether mothers had fertility treatments or prior pregnancy losses, factors that may contribute to postnatal depressive symptoms (Li, Lui, & Odouli, 2009; Sheard et al., 2007). In addition, the analyses focusing on family support relied on a smaller subsample of families, possibly underestimating effects (although family support was statistically significant in all models assessed). Moreover, the support measure assessed receipt of support from family members related to their maternal role rather than their satisfaction with the support provided. Finally, because we focused on Time 1 time invariant risks that would lend themselves to early identification and screening of maternal depression, in this report we did not focus on dynamic family processes such as quality of infant-mother interactions or whether the child was eventually diagnosed with a disability. We are continuing to investigate these factors in our sample of PT LBW infants as they reach school age. Despite these limitations, our investigation provided crucial information about predictors of maternal depression trajectories in a high risk sample, including identification of factors that could be examined as possible screening targets for PT LBW infants and their families.

Acknowledgments

This research was supported by grants from the National Institutes of Health (HD44163) and the University of Wisconsin. Special thanks to the children and families who generously gave of their time to participate in this study.

Footnotes

Publisher's Disclaimer: The following manuscript is the final accepted manuscript. It has not been subjected to the final copyediting, fact-checking, and proofreading required for formal publication. It is not the definitive, publisher-authenticated version. The American Psychological Association and its Council of Editors disclaim any responsibility or liabilities for errors or omissions of this manuscript version, any version derived from this manuscript by NIH, or other third parties. The published version is available at www.apa.org/journals/fam.

Contributor Information

Julie Poehlmann, University of Wisconsin-Madison.

AJ Miller Schwichtenberg, University of California at Davis.

Daniel Bolt, University of Wisconsin-Madison.

Janean Dilworth-Bart, University of Wisconsin-Madison.

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