Oral contraceptives taken just before or during pregnancy do not increase the risk of birth defects, according to a study by researchers from HMS, Harvard T.H. Chan School of Public Health, and the Statens Serum Institut in Denmark. The study was published January 6, 2016, in BMJ.
The researchers found that for the pregnant women in the study the prevalence of major birth defects was consistent—about 25 per 1,000 live births—regardless of contraceptive use.
“Women who become pregnant either soon after stopping oral contraceptives or while taking them should know that this exposure is unlikely to cause their fetus to develop a birth defect,” says Brittany Charlton, an HMS instructor in pediatrics at Boston Children’s Hospital and a researcher in the Harvard Chan School Department of Epidemiology.
When used diligently oral contraceptives are more than 99 percent effective: Nearly 10 percent of women, however, become pregnant within their first year of use. Many other women stop using oral contraceptives when planning a pregnancy and conceive within a few months.
While previous studies of the potential health risks to children exposed in utero to the hormones have relied primarily on women recalling their past oral contraceptive use, Charlton and colleagues were given access to a wealth of data collected from multiple Danish health registries between 1997 and 2011. These data were linked to individuals by the unique personal identification number that each Denmark resident is assigned. The researchers looked at data on more than 880,000 live-born infants and their health one year later. Oral contraceptive use by the mother was estimated based on the date of her most recently filled prescription.
Among the women in the study population, 69 percent had stopped using oral contraceptives more than three months before becoming pregnant, while 8 percent had discontinued use within three months of becoming pregnant. One percent, more than 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 as induced abortions.
Image: John Soares; the Warren Anatomical Museum in the Countway Library of Medicine (object)