What the New Acetaminophen-in-Pregnancy Study Found—and What Clinicians Still Recommend
Summary: This explainer covers the key findings from the Danish acetaminophen-in-pregnancy study, the statistical limits of those findings, and why clinicians say the drug remains safe when used for fever or severe pain.
A study of about 300 infant girls in Denmark found that girls whose mothers took paracetamol—known as acetaminophen in North America and sold under brands like Tylenol—during pregnancy had smaller ovaries at three months old, on average. Infant boys exposed before birth also had smaller testes on average. Researchers in Copenhagen measured the infants’ reproductive organs with ultrasound.
Among the girls exposed to acetaminophen in the womb, average ovarian volume was about 40% smaller, uterine volume about 13% smaller, and the number of ovarian follicles—the sacs that nurture immature eggs—about 23% lower, compared with girls not exposed. Higher doses were linked to bigger differences, although no mother in the study went beyond the recommended daily maximum of 4,000 milligrams.
The team also analyzed data from another study of 1,210 girls born in Copenhagen between 1997 and 2002 and found a link between fetal exposure to paracetamol and smaller ovaries during adolescence.
Those findings do not prove that acetaminophen caused the differences. The association could reflect the underlying conditions that led women to take the drug. Infections, pain, and fever can affect fetal development in their own ways, and women who are sicker may take more medication. There is also a statistical risk: the researchers ran multiple analyses, and with each additional analysis the chance of finding a significant association by random error grows.
Nor is it clear what smaller ovaries or testes in infancy mean later. The study cannot confirm that those size differences affect fertility in adulthood.
Clinicians have not changed their advice. Margit Bistrup Fischer at Copenhagen University Hospital–Rigshospitalet says women should still use paracetamol when they have high fever or strong pain, because avoiding it in those situations carries risks. What she wants is more dialogue. Most women in the study took the painkiller for headaches or musculoskeletal discomfort rather than fever, and some of that pain could be managed with rest, heat treatment, or physiotherapy. “We should have a dialogue about when paracetamol is actually necessary,” she says.
Dimitrios Siassakos at University College London put it more bluntly: “This paper would not change my practice or advice.”
Acetaminophen remains one of the most commonly used medications during pregnancy, and this study adds a measured data point to a growing debate about its safety. It does not establish harm. It does suggest that even a widely trusted drug deserves case-by-case judgment—and that long-term studies are needed to learn whether early size differences matter for future fertility.
For now, the practical takeaway is subtle: keep treating genuine fever and severe pain, but ask whether a mild ache really needs medication. The evidence supports careful use, not alarm.