Oral Contraceptive Use Before and During Pregnancy Appears Safe

Lara C. Pullen, PhD

January 07, 2016

Maternal use of oral contraceptives just before pregnancy or during pregnancy does not appear to increase the risk for birth defects. The results suggest that women who have a breakthrough pregnancy during oral contraceptive use are unlikely to have a fetus with a major birth defect.

Brittany M. Charlton, ScD, from the Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, and colleagues published the results of their prospective observational cohort study online January 6, 2016, in the BMJ. They used Danish registry records from 1997 to 2011 (880,694 live births) and prospectively collected prescription data on the use of oral contraceptives. The investigators assumed that women who filled their prescriptions were exposed to oral contraceptives.

For analysis purposes, women were placed into one of four oral contraceptive exposure groups: never users, use more than 3 months before pregnancy onset, use 0 to 3 months before pregnancy onset, and use after pregnancy onset.

Because major birth defects are rare outcomes, the investigators grouped the birth defects into categories such as limb defects.

Prevalence of major birth defects held steady at approximately 25 per 1000 births across all oral contraceptive exposure groups. The researchers found no significant increase in risk for subgroups of defects from oral contraceptive exposure.

The study lacked the statistical power, however, to examine specific oral contraceptive formulations and certain birth defect subgroups (gastroschisis and hypoplastic left heart syndrome). The investigators also lacked information about folate exposure.

"Overall, our study confirms the bulk of the previous work documenting no increase in birth defects following oral contraceptive exposure. Because previous studies have reported increased risks for specific defects including hypoplastic left heart syndrome, gastroschisis, limb defects, and urinary tract anomalies, we did examine each of these separately. Our study did not find significantly increased risks for any of these four birth defect categories, although each of our analyses should be interpreted in the context of statistical precision," the authors note.

The study adds to a body of literature on the subject, but the researchers acknowledge that comparisons between studies are difficult, given the wide variation in the time windows of oral contraceptive exposure. A few of the published studies have found that specific major birth defects, such as limb defects, are associated with maternal oral contraceptive use.

The authors have disclosed no relevant financial relationships.

BMJ. Published online January 6, 2016. Full text

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