Objective: To determine the association between combined monophasic oral contraceptive (OC) use and primary infertility.
Design: Case-control.
Setting: Women serving as controls of the Cancer and Steroid Hormone Study.
Participants: Women were 19 to 40 years of age at first conception or infertility diagnosis. Based on 24 consecutive months of unprotected intercourse without a recognized conception, 419 nulligravid women had primary infertility; controls were 2,120 fertile women. A calendar of each women's reproductive history was used to determine fertility status and contraceptive use before infertility diagnosis or first conception.
Main outcome measure: Primary infertility.
Results: Combined monophasic OC use was associated with a lower frequency of primary infertility, particularly among younger (age 20 years) compared with older women (age 30 years) after adjusting for barrier method use and education. A similar association was found for duration of OC use. When adjusted for age at first conception or infertility and barrier method, both higher (> 50 micrograms) and lower (< or = 50 micrograms) estrogen dose use were associated with decreased risk of primary infertility.
Conclusion: Combined monophasic OC use was associated with a lower frequency of primary infertility.
PIP: Researchers compared data on 419 nulligravid US women diagnosed with primary infertility (no conception during 24 consecutive months of unprotected intercourse) with data on 2120 fertile women to examine the relationship between use of combined monophasic oral contraceptives (OCs) and primary infertility. All cases had documented reproductive histories from menarche to menopause for contraceptive methods before infertility. Controls were more likely than infertile women to have used OCs (14.2% vs. 9.07%; unadjusted odds ratio [OR] = 0.6) and to have used OCs longer (33.6 vs. 30.1 months; OR = 0.6). Infertile women were just as likely as fertile women to have used high-estrogen-dose OCs (i.e., 50 mcg) (5.28% vs. 8.52%). Fertile women were more likely than infertile women to have used barrier methods (41.8% vs. 17.2%; OR = 0.29). When the researchers adjusted for education and barrier method use, infertile women were still less likely to have used OCs than fertile women, especially women who were 20 years old at first conception or infertility (adjusted OR [AOR] = 0.27) (AOR = 0.68 for older women). Both high- and low-estrogen-dose OCs were associated with a reduced risk of primary infertility (AOR = 0.48 for or= 50 mcg and 0.4 for 50 mcg). These results suggest that combined OC use reduces the risk of primary infertility, especially among younger women, regardless of duration of use or estrogen dose.