Trump Warned Pregnant Women Over Tylenol, New Study Finds 40% Smaller Ovaries in Daughters

A Danish study has found that girls exposed to paracetamol during pregnancy had differences in reproductive development, with those exposed before 17 weeks having an average ovarian volume around 40 per cent smaller than girls whose mothers did not use the painkiller.

Published in Human Reproduction Open, the study examined 302 three-month-old girls whose mothers' paracetamol use had been tracked during pregnancy. Researchers also found about 23 per cent fewer ovarian follicles among girls exposed from 17 weeks onwards, although the observational research cannot establish that paracetamol caused the differences.

The findings come amid debate over paracetamol use during pregnancy following Donald Trump's warnings in 2025 that pregnant women should limit Tylenol over a claimed link with autism. However, the Danish study did not examine autism or other neurodevelopmental conditions and does not provide evidence for or against that separate claim.

Study Finds Differences In Ovarian Development

The study, led by Margit Bistrup Fischer of Rigshospitalet in Copenhagen, tracked mothers' paracetamol exposure during pregnancy before assessing reproductive development in their daughters.

Girls exposed before 17 weeks had an average 40 per cent smaller ovarian volume and 13 per cent smaller uterine volume than those whose mothers had not reported using paracetamol. Among girls exposed later in pregnancy, researchers found about 23 per cent fewer ovarian follicles.

A separate group of 1,210 girls was followed from infancy into adolescence. Prenatal exposure was associated with smaller uteruses at puberty and smaller ovaries during adolescence, although the researchers said further research was needed to determine whether such differences have lasting consequences.

The researchers stressed that the findings do not show that prenatal paracetamol exposure causes reduced fertility. They said longer-term studies would be needed to establish whether the differences persist into adulthood or affect reproductive health.

Experts Question Clinical Significance

The research was observational, meaning it cannot establish a direct cause-and-effect relationship. Mothers who took paracetamol may also have had medical conditions or other characteristics that influenced foetal development.

Professor Dimitrios Siassakos, an obstetrics and gynaecology specialist at University College London, questioned the clinical significance of the findings and said the study had not accounted for all possible confounding factors. He also noted that the number of statistical comparisons increased the possibility that some results could have occurred by chance.

Dr Adam Brentnall, a biostatistician at Queen Mary University of London, said the study raised an important question but that the strength of its conclusions was not fully supported by the statistical evidence. He said it remained unclear whether the observed differences would affect ovarian function or reproductive lifespan.

The researchers said their findings were consistent with previous animal studies but called for further research before conclusions could be drawn about long-term reproductive effects.

UK Guidance On Paracetamol Remains Unchanged

UK NHS guidance states that paracetamol is usually the first-choice painkiller during pregnancy and advises taking it for the shortest possible time.

Trump's earlier warnings concerned separate research into possible neurodevelopmental effects. In September 2025, the US Food and Drug Administration said studies had reported an association between prenatal acetaminophen exposure and conditions including autism and ADHD, but stressed that a causal relationship had not been established and that contrary studies existed.

The Danish researchers have said women should not be alarmed by the findings. Further research will be needed to establish whether the reproductive differences observed in infancy have any lasting consequences.