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Oral contraceptive use before pregnancy not linked to birth defects

Exposure to oral contraceptives just before or during pregnancy does not significantly increase the risk for major birth defects, according to a study published in the British Medical Journal.

“Despite decades of research on the safety of oral contraceptive use, little is known about the association of oral contraceptive use just before or during pregnancy with the offspring’s health,” Brittany M. Charlton, MSc, ScD, an instructor in the department of epidemiology at the Harvard T.H. Chan School of Public Health, and colleagues wrote. “In particular, it is unclear whether these circulating exogenous sex hormones can harm the fetus and how long potential effects of circulating exogenous sex hormones might last.”

To investigate whether oral contraceptive use within 3 months prior to pregnancy, or use during early pregnancy, is associated with an increased risk for birth defects, the researchers conducted a prospective, observational cohort study, using contraception and birth defect data collected for 880,694 live births from Danish registries between 1997 and 2011. Assuming that oral contraceptive exposure lasted up to the most recently filled prescription, the researchers performed a logistic regression estimating prevalence odds ratios of any major birth defect and categories of birth defect subgroups.

The main outcome measure was the number of major birth defects throughout the 1-year follow-up, defined according to the European Surveillance of Congenital Anomalies classification.

According to the researchers, 69% of the mothers had used oral contraceptives but stopped more than 3 months before pregnancy onset; this was the reference group. Another 8% had recently ceased contraceptive use within 3 months of pregnancy. In addition, 21% had never used oral contraceptives, and 1% used them beyond pregnancy onset. The groups who had used oral contraceptives within 3 months of pregnancy onset and beyond were considered exposed.

Of the 880,694 infants included in the study, 2.5% were diagnosed with a major birth defect within the first year of life. The prevalence of major birth defects per 1,000 births was consistent across all groups: 25.1 for those who never used oral contraceptives, 25 for those who used oral contraceptives 3 months before pregnancy onset, 24.9 for use within 3 months of pregnancy onset and 24.8 for those who used oral contraceptives after pregnancy onset.

The researchers found no increase in the prevalence of major birth defects with oral contraceptive exposure among mothers with recent use before pregnancy (OR = 0.98; 95% CI, 0.93-1.03), or after pregnancy onset (OR =  0.95; 95% CI, 0.84-1.08) compared with the reference group. In addition, there was no increase in prevalence of any birth defect subgroup.

“We did not observe a significantly increased risk of major birth defects associated with oral contraceptive use in the months before or after pregnancy onset,” Charlton and colleagues wrote. “For women who have a breakthrough pregnancy during oral contraception use or even intentionally become pregnant within a few months of stopping oral contraceptive use, any exposure is unlikely to cause her fetus to develop specific major birth defects.” – by Jason Laday

Disclosure: The authors report no relevant financial disclosures.