Contraceptives don’t cause birth defects
© 2016 Roy Benaroch, MD
A huge, well-designed Danish study should finally put one concern about oral contraceptive pills to rest. They do not increase the risk of birth defects.
Wait a minute, you might say—birth defects? Those pills are supposed to prevent pregnancy—and if you don’t get pregnant, who cares about birth defects? It turns out that though oral contraceptive pills (OCPs) are about 99% effective in preventing pregnancy in medical studies, in real-world use they fail about 10% of the time over a year of use (that is, about 10% of women relying on OCPs become pregnant during a year of use.) This happens because people sometimes skip pills, or experience drug-drug interactions. So it’s common that women taking OCPs (or who recently stopped OCPs) become pregnant.
There have been several previous studies that have shown mixed results, though those studies were much smaller and often relied on self-reporting of OCPs use and birth defects. In the new study, published in January 2016 in BMJ, researchers evaluated all live births in Denmark from 1997-2011. Pharmacy records were used to see which women had pilled prescriptions for oral contraceptives. They ended up with almost 900,000 births with complete records. The rates of birth defects were essentially identical among all of the groups:
- Never used OCPs: 25.1 birth defects per 1,000 births
- Used OCPs more than 3 months before pregnancy: 25.0
- OCP use 0-3 months before pregnancy: 24.9
- OCP use during early pregnancy: 24.8
Striking, isn’t it? All of those numbers were statistically identical (that is, within the expected margin of error.) OCP use whether immediately before or during pregnancy did not increase the risk of birth defects.
We’ve got to hand it to the Danes. Their robust national health database and meticulous record-keeping has allowed us to look at huge populations, to find even small markers of risk. A classic 2002 study from the NEJM showed that in a cohort of half a million Danish children, MMR vaccine did not increase the risk of autism. Studies that large are a great way to uncover evidence of even tiny risks. It’s very reassuring that OCPs (and the MMR vaccine) are not things parents need to worry are hurting their babies.