A study found that women who use Tylenol, which contains acetaminophen, during pregnancy may have daughters with smaller ovaries and uteruses and fewer ovarian follicles at birth. However, the findings show only an association and do not prove the medication caused the changes or that they will affect future fertility.

According to Reuters, the study was led by Margit Bistrup Fischer of Rigshospitalet in Copenhagen. Researchers examined medication exposure during fetal development and reproductive organs after birth, finding smaller ovaries and uteruses and fewer ovarian follicles among girls exposed to Tylenol.

Previous animal studies have linked acetaminophen exposure in the womb to changes in reproductive organ development. Whether similar differences in humans persist into adulthood or affect fertility remains unknown.

Researchers said long-term follow-up is needed to determine whether the differences seen in infancy affect reproductive health, including future fertility and the age at menopause.

Because the study was observational, other factors may have contributed to the findings, so it cannot establish a cause-and-effect relationship.

Acetaminophen is widely used for pain and fever. The findings do not mean pregnant women should stop or change medication without medical advice. Further research is needed to determine whether fetal exposure has lasting effects on reproductive health.