Table 4Summary of evidence

No. of studiesDesignLimitationsConsistencyApplicabilityOverall QualitySummary of FindingsComment
KQ1. Does screening for GDM lead to a reduction in perinatal morbidity and mortality for mother and/or infant?
A. During the 1st trimester up to 24 weeks gestation?
No evidence
B. After 24 weeks gestation?
No evidence
KQ2. What are the reliabilities and yields of current screening tests for GDM?
A. During the 1st trimester and up to 24 weeks gestation?
No evidence
B. After 24 weeks gestation?
No evidence
KQ3. Does treatment for GDM lead to a reduction in perinatal morbidity and/or mortality for mother and/or infant?
Treated vs. Untreated
239,44RCTNo serious limitations. 1 of 2 RCT occurred 40 years ago when ability to achieve tight glucose control was limitedNo inconsistenciesStudies conducted in Inner-city Boston (race/ethnicity NR) and Australia (75 percent Caucasian).GoodMaternal: Only reported in 1 study; gestational hypertension reduced with treatment compared to no treatment (Adj RR 0.70 [0.51–0.95])

Neonatal: Composite outcome (stillbirth, neonatal death, shoulder dystocia, bone fracture, and nerve palsy) reduced with treatment of mild GDM compared to no treatment (Adj RR 0.33 [0.14–0.75]); 0 vs. 5 stillbirths/neonatal deaths with treatment vs. no treatment. Older study did not find a significant difference in perinatal mortality (only macrosomia improved with treatment).
Both used 50 g GCT; Recent study used 75g diagnostic OGTT and only included women with mild GDM (2 hr OGTT < 200 mg/dL).
Trials of treatment comparisons
638,4043,47RCT3 of the 6 studies evaluated <75 womenStudies varied in treatment tested but none had serious inconsistencies with other trials regarding outcomes4 of 6 trials included predominantly Hispanic women and limited numbers of other ethnic groupsFairMaternal: None reported maternal death or found significant differences in gestational hypertension with treatment.

Neonatal: Outcomes either did not differ with treatment or improved if treatment improved glycemic control (e.g., neonatal hyperbilirubinemia and hypoglycemia).
No evidence available for metformin. The MiG trial (Metformin in Gestational Diabetes) is in progress.
Diagnosis and Treatment prior to 24 weeks gestation
145Prospective cohortDefinition of hypertension categories not providedNot applicableConducted in SpainFairMaternal: Women with early-onset GDM (1st antenatal visit) were significantly more likely to have pre-existing chronic hypertension, hypertension, combined pre-eclampsia (pre-eclampsia and superimposed pre-eclampsia) then those diagnosed >24 weeks

Neonatal: Neonates of women with early-onset were more likely to have perinatal death and hypoglycemia.
KQ4. What are the adverse effects of screening for GDM?
349512 prospective cohort; 1 cross-sectionalNo serious limitations. Studies do not attempt to isolate the psychological impact of antenatal surveillance, such as the modified biophysical profile. Antenatal surveillance is presumed to be more common among women with GDM and thus represented by the diagnosis itself.No serious inconsistencies2 Australian and 1 US study, all included primarily Caucasian womenFairMaternal: Limited data are mixed on whether anxiety/QOL is worsened in the first several weeks after screening. The RCT found no differences between women who screened positive vs. negative in measures of anxiety, depression, or concern for baby's health immediately after screening or later in pregnancy. The prospective cohort found health perceptions (in a minority of self-reported health domains) were worse at 30 weeks gestation among screen positive women, but did not differ at 36 weeks gestation or 6 weeks postpartum. The cross-sectional study found no differences in anxiety or depression at 35 weeks.

Neonatal: No adverse effects identified in the literature.
KQ5. What are the adverse effects of treatment of GDM?
73843,56RCT, 1 Prospective CohortLimited data available and only 2 of the studies included >100 women with GDM.No serious inconsistencies1 RCT is Australian, but reasonably representative of US primary care practice, with 75 percent Caucasian. The remaining studies included primarily Hispanic women.FairMaternal: No maternal deaths were reported. Significant maternal hypoglycemia was rarely reported, irrespective of treatment modality. There was no evidence supporting psychological harm with treatment. On the contrary, one RCT found a significant reduction in postpartum depression (based on the Edinburgh Postnatal Depression Scale questionnaire) among women treated for GDM compared to no treatment (Adj RR 0.46 [0.29–0.73]).
Neonatal: Limited data in small studies found no harm to the fetus nor placental transfer of glyburide or lispro insulin; We found no quality data on other potential harms to the offspring associated with maternal treatment of GDM.
No data is available for metformin.

N/A-not applicable; GDM-gestational diabetes mellitus; RCT-randomized controlled trials; NR-not reported; Adj RR-adjusted relative risk; GCT-glucose challenge test; OGTT-oral glucose tolerance test; QOL-quality of life

From: 3, Critical Key Questions & Results

Cover of Screening for Gestational Diabetes Mellitus
Screening for Gestational Diabetes Mellitus [Internet].
Evidence Syntheses, No. 60.
Hillier TA, Vesco KK, Whitlock EP, et al.

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