Humans have been trying to avoid pregnancy for thousands of years, and while primitive birth control methods were often ineffective and dangerous, modern birth control is generally always safe and successful when used properly. However, some still worry that continuing to take birth control before or after pregnancy may yield some risks to the fetus.

Oral contraceptives occasionally come with minor risks, but birth defects during pregnancy don't seem to be one of them, according to a new study out of the Harvard T.H. Chan School of Public Health. In collaboration with the Statens Serum Institut in Denmark, Harvard researchers found using birth control before and during pregnancy doesn't seem to affect the risk for birth defects.

"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," Brittany Charlton, a researcher at the Harvard Chan School Department of Epidemiology and an author of the study, said in the press release. "This should reassure women as well as their health care providers.

The study examined data from Danish health registries, dating from 1997 to 2011. They reviewed 880,694 infants at their birth and one year later as a follow-up. The data also showed the last time a mother had filled a birth control prescription; and while this may hint that some women continued using birth control during pregnancy, it didn’t necessarily guarantee they did. Further research would be needed to examine this issue, but to be safe, researchers recommend women stop taking oral birth control once they become pregnant.

Researchers also found that one-fifth of the pregnant women examined had never used oral contraceptives; two-thirds had stopped using them three months before becoming pregnant; and 8 percent of them had stopped using them within three months after becoming pregnant. They found that the prevalence of birth defects occurred consistently among all of these groups, showing that the birth control didn't contribute at all to the risk.

Occasionally, women become pregnant even while they're on birth control, meaning they often continue using it until they find out they're pregnant. For women who have experienced this, the study aims to ease their minds about the concerns of potential birth control risks — not much research exists about how the hormones in contraceptives affect fetuses.

Past research linked birth control pills with birth defects, like low birth weight, congenital urinary tract problems, or premature births. But follow-up research didn't find any concerning link between birth control and these defects.

Oral contraceptives have also been linked to other potential health complications, like an increased risk for ischemic stroke, brain structure changes, migraines, and high blood pressure. One recent study also examined the link between certain women taking oral contraceptives and their increased risk of HIV.

However, it's safe to say that the risk of developing any of these problems from birth control taken properly is extremely low.

Source: Charlton B, Mølgaard-Nielsen D, Svanström H, Wohlfahrt J, Pasternak B, Melbye M. Maternal use of oral contraceptives and risk of birth defects: nationwide cohort in Denmark. BMJ. 2016.