There’s some good news for pregnant women: Don’t worry if you took birth control pills before your pregnancy was confirmed.

A new study has found that that taking birth control pills during the early stages of pregnancy is not associated with an increased risk of birth defects.

This is important because many women don’t know they are pregnant for several weeks, until symptoms prompt them to get a pregnancy test. About 16 percent of women of childbearing age in the United States take the pill. While the failure rate is low, it can increase due to missed doses, drug interactions or illness.

Researchers studied more than 880,000 births in Denmark, and found that the overall rate of birth defects was the same for women who had never taken the pill and for women who had taken the pill, even those who took it early in their pregnancy. The findings, by Harvard University School of Public Health researchers, were published in the medical journal BMJ. The lead researcher called the results convincing evidence that there’s no link between oral contraceptives and birth defects.

The rate of birth defects across all groups of mothers, whether or not they took birth control pills, is about 25 per 1,000 births.

Doctors don’t always know what causes a birth defect, but genetic problems, environmental factors, illness or alcohol and drug use can affect a baby’s development.

Pregnant women should see a physician regularly, make sure they are getting the recommended amount of folic acid, avoid alcohol and drugs, and maintain a healthy lifestyle and diet.

But for women who are worried because they took birth control pill early in their pregnancy, there appears to be no harm done.