Public Release: 

Oral contraceptive use not associated with increased birth defects risk

Harvard T.H. Chan School of Public Health

Boston, MA - Oral contraceptives taken just before or during pregnancy do not increase the risk of birth defects, according to a new study by researchers from Harvard T.H. Chan School of Public Health and the Statens Serum Institut in Denmark. They found that the prevalence of major birth defects was consistent (about 25 per 1,000 live births) across all pregnant women in the study population regardless of contraceptive use.

"Women who become pregnant either soon after stopping oral contraceptives, or even while taking them, should know that this exposure is unlikely to cause their fetus to develop a birth defect," said first author Brittany Charlton, a researcher in the Harvard Chan School Department of Epidemiology and instructor at Harvard Medical School and Boston Children's Hospital. "This should reassure women as well as their health care providers."

The study will appear online January 6, 2016 in BMJ.

Even though oral contraceptives are more than 99% effective with perfect use, almost 10% of women become pregnant within their first year of use. Many more women will stop using oral contraceptives when planning a pregnancy and conceive within a few months. Little is known about the potential health effects to children from in utero exposure to the hormones in oral contraceptives.

While previous studies have primarily relied on women recalling their past oral contraceptive use, Charlton and colleagues were able to tap into a wealth of data collected from multiple Danish health registries between 1997 and 2011 and linked by the unique personal identification number assigned to all Denmark residents. The researchers looked at 880,694 live-born infants, and the health of these children at one-year follow-up. Oral contraceptive use was estimated based on the date of the mother's most recently filled prescription.

Among the women in the study population, a fifth had never used oral contraceptives before becoming pregnant, and more than two-thirds had stopped using oral contraceptives at least three months before becoming pregnant. Eight percent had discontinued use within three months of becoming pregnant, and 1%, or well over 10,000 women, had used oral contraceptives after becoming pregnant.

The prevalence of birth defects was consistent across each category of oral contraceptive use, and remained so when the researchers added in pregnancies that ended as stillbirths or induced abortions.

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Charlton was supported by funds from Harvard Chan School's Maternal Health Task Force and Department of Epidemiology Rose Traveling Fellowship; the training grant T32HD060454 in reproductive, perinatal, and pediatric epidemiology and award number F32HD084000, both from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health; and the training program in cancer epidemiology under grant T32CA09001 from the National Cancer Institute, National Institutes of Health.

"Maternal use of oral contraceptives and risk of birth defects: nationwide cohort in Denmark," Brittany M. Charlton, Ditte Mølgaard-Nielsen, Henrik Svanström, Jan Wohlfahrt, Björn Pasternak, Mads Melbye, BMJ, online January 6, 2016, doi: 10.1136/bmj.h6712

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Harvard T.H. Chan School of Public Health brings together dedicated experts from many disciplines to educate new generations of global health leaders and produce powerful ideas that improve the lives and health of people everywhere. As a community of leading scientists, educators, and students, we work together to take innovative ideas from the laboratory to people's lives--not only making scientific breakthroughs, but also working to change individual behaviors, public policies, and health care practices. Each year, more than 400 faculty members at Harvard Chan School teach 1,000-plus full-time students from around the world and train thousands more through online and executive education courses. Founded in 1913 as the Harvard-MIT School of Health Officers, the School is recognized as America's oldest professional training program in public health.

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