A study led by Margit Bistrup Fischer of Rigshospitalet found infant girls exposed to paracetamol in the womb showed smaller reproductive organs and fewer ovarian follicles.
Three-month-old girls exposed in utero had on average 40 per cent smaller ovarian volume, 13 per cent smaller uterine volume, and 23 per cent fewer follicles.
Researchers stressed the observational study does not prove paracetamol causes these anatomical changes or leads to impaired future fertility.
Female reproductive organ development may be affected by a mother’s use of Tylenol or generic paracetamol during pregnancy, Danish researchers reported on Wednesday. But they stressed that the study does not prove the medicine caused the changes or show any effect on future fertility.
Margit Bistrup Fischer of Rigshospitalet in Copenhagen, who led the study, said in a statement that women who used the medicine while pregnant should not be alarmed. She added that only long-term follow-up can show whether the differences matter later in life, including for age at menopause as per Reuters.
The study points to differences in infant girls’ ovaries, uteruses and hormone levels after fetal exposure to the drug. Current medical guidance still recommends paracetamol or acetaminophen as safe for pain and fever in pregnancy, partly because untreated high fever or severe pain can themselves pose risks to the mother and fetus.
Study Design Details
The team tracked 302 girls aged 3 months.
Fischer’s group studied 302 infants whose mothers’ use of the drug during pregnancy had been monitored. The participants did not report which manufacturer’s product they had used.
Of the 302 infants, 92 were first exposed before 17 weeks of pregnancy and 67 were first exposed after 17 weeks. Another 143 were born to mothers who had not used the drug.
Doses remained low across the cohort. Researchers tracked intake of the Danish-market drug using periodic urine tests and mother-completed questionnaires. Every mother stayed below the daily ceiling of 4,000 milligrams, turning to the painkiller primarily for headaches or musculoskeletal discomfort.
Measured Organ Changes
The reported differences were sizeable. Researchers reported in Human Reproduction Open on Wednesday that infants exposed in the womb had smaller ovaries, fewer ovarian follicles, smaller uteruses and lower reproductive hormone levels. Ovarian follicles are the structures that contain immature eggs.
Among the 3-month-old girls exposed in utero, ovarian volume was 40 per cent smaller on average, uterine volume was 13 per cent smaller and ovarian follicles were 23 per cent fewer, the study found. Girls first exposed before 17 weeks of pregnancy also had a lower average Anti-Müllerian hormone level, a marker of the amount and quality of eggs in the ovaries.
The team also examined a separate group of 1,210 girls who were followed from infancy to adolescence and whose mothers had reported paracetamol use during pregnancy. In that group, fetal exposure was associated with smaller uteruses at puberty and smaller ovaries during adolescence.
Context And Reactions
The biological context matters. A woman’s reproductive function and reproductive window are set while she is still in the womb, the researchers explained, and girls are born with all the eggs they will ever have. Animal studies have suggested that fetal exposure to the medicine may affect ovarian egg reserve and later reproductive function, but similar findings had not previously been reported in humans.
Brand owner Kenvue defended the medicine. The company, which makes Tylenol, advised expectant or nursing mothers in an email to consult healthcare professionals before using acetaminophen—known as paracetamol in Europe.
Kenvue stated the painkiller remains the most researched and safest choice for pregnancy. It highlighted methodological limits in the study, stating the findings do not establish a causal link to infant reproductive growth. Company shares fell more than 3 per cent.
Fischer said the study cannot predict outcomes for any individual woman or child. She noted that many women who used the drug during pregnancy had daughters whose ovarian measurements were similar to those of daughters born to women who did not use the medicine.
Current guidelines continue to recommend paracetamol or acetaminophen for treating pain and fever during pregnancy. Fischer said untreated high fever or severe pain can themselves pose risks to the mother and fetus.
US President Donald Trump has linked Tylenol use during pregnancy to autism, a claim the medical community and major health organisations have widely dismissed as lacking scientific backing.
The findings align with animal research. Dr Christian De Geyter, a reproductive medicine specialist at the University Hospital of Basel in Switzerland, said in an accompanying commentary that doctors should monitor exposed girls through menopause. Health officials must also re-evaluate pregnancy guidance on taking the painkiller, he added.
