Exposure to acetaminophen in the womb may be linked to differences in how a girl’s reproductive system develops.Acetaminophen—the active ingredient in Tylenol—is commonly used to treat pain and fever during pregnancy.Researchers in Denmark examined 302 baby girls at about 3 months old.Those exposed to acetaminophen before birth had, on average, smaller ovaries and uteruses and fewer ovarian follicles — the structures that contain immature eggs.Girls exposed exclusively in early fetal life also had lower levels of a hormone used as a marker of ovarian egg reserve.A separate group followed longer showed similar differences: smaller uteruses at puberty and smaller ovaries during adolescence.The study was observational and does not prove acetaminophen caused the differences, but the researchers note the results are consistent with previous animal studies.The lead author stresses that women who used acetaminophen during pregnancy should not be alarmed, and the findings should not discourage women from using it when medically needed.She says, “Whether the differences observed in our study have implications for fertility and age at menopause in humans remains unknown and will require long-term follow-up of the girls in our cohort.”The advice for now: decisions about pain management during pregnancy should be made with your healthcare provider. Source: Human Reproduction OpenAuthor Affiliations: Rigshospitalet, EDMaRC, University of Southern Denmark, University of Edinburgh, University of Copenhagen, Roskilde University.Sign up for our weekly HealthDay newsletter