Tylenol use during pregnancy has been associated with reproductive-organ differences in daughters, although researchers stressed that the observational findings neither establish causation nor predict future fertility.
Published in Human Reproduction Open, the research examined 302 three-month-old girls whose mothers’ use of Tylenol was monitored through urine samples collected at regular intervals during pregnancy. Tylenol is also sold as acetaminophen and is known as paracetamol outside the U.S.
The study included 92 infants first exposed before 17 weeks of pregnancy and 67 first exposed after 17 weeks. Another 143 were born to mothers who had not used the medicine. The mothers generally took relatively low amounts, most commonly for headaches or musculoskeletal pain, and none exceeded the recommended daily maximum of 4,000 milligrams.
Among girls exposed in the womb, average ovarian volume was 40% smaller, uterine volume was 13% smaller and the number of ovarian follicles was 23% lower. Ovarian follicles contain immature eggs. Exposure before 17 weeks was also associated with lower Anti-Müllerian hormone levels, described by the researchers as an indicator of the quantity and quality of eggs in the ovaries.
A separate group of 1,210 girls was followed from infancy into adolescence. In that group, mothers’ reported use of Tylenol during pregnancy was associated with smaller uteruses at puberty and smaller ovaries during adolescence.
Margit Bistrup Fischer of Rigshospitalet in Copenhagen, who led the study, said the results should not alarm women who used Tylenol while pregnant. The research cannot determine the outcome for an individual child, and many exposed girls had ovarian measurements comparable with those recorded among girls whose mothers had not taken the drug.
Long-term follow-up will be required to establish whether the observed differences have any implications for fertility or the timing of menopause. The researchers explained that female reproductive function develops in the womb and that girls are born with all the eggs they will have, but the study did not establish that the measured differences would affect later reproductive outcomes.
Christian De Geyter, a reproductive medicine specialist at the University Hospital of Basel, said in an accompanying commentary that the findings were consistent with evidence from animal research. He called for girls exposed in the womb to be followed into menopause and argued that recommendations covering Tylenol use during pregnancy should be reconsidered.
Current guidelines continue to recommend Tylenol as safe for treating pain and fever during pregnancy. Fischer also warned that untreated high fever or severe pain can pose risks to the mother and fetus.
U.S. President Donald Trump has separately linked Tylenol use during pregnancy with autism. That claim has been widely dismissed by the medical community and major health organisations as lacking scientific support.
The operational issue is therefore continued evidence monitoring rather than a confirmed change in treatment practice. Existing guidance remains in place, while follow-up extending into menopause could determine whether recommendations on Tylenol use during pregnancy require revision.
