A Danish study published this month has found that infant girls exposed to paracetamol before birth had measurably smaller ovaries and wombs at three months old than girls whose mothers avoided the drug during pregnancy, a finding researchers say raises questions but falls well short of proving the common painkiller causes lasting harm.
The research, led by Dr. Margit Bistrup Fischer at Copenhagen University Hospital–Rigshospitalet and published in the journal Human Reproduction Open, tracked 685 pregnant women who reported their paracetamol use every two weeks and provided urine samples in the first trimester. Researchers then examined 302 of the resulting daughters by ultrasound at three months of age.
What the numbers showed
Girls exposed to paracetamol before 17 weeks of pregnancy had, on average, 40 percent smaller ovarian volume, 23 percent fewer ovarian follicles and 13 percent smaller uterine volume than unexposed girls, along with lower levels of anti-Müllerian hormone, a marker tied to egg supply. A second, larger validation group of 1,210 girls followed from infancy into adolescence showed a similar pattern of smaller uteruses at puberty and smaller ovaries in the teenage years.
When the babies were three months old, we found that those who had been exposed to paracetamol during foetal life had, on average, a 40% smaller ovarian volume, a 13% smaller uterine volume and 23% fewer ovarian follicles.
Dr. Margit Bistrup Fischer, Copenhagen University Hospital–Rigshospitalet
Fischer stressed that the study "does not establish a direct cause-and-effect relationship" and urged pregnant women not to be alarmed by the results, which are observational and cannot rule out other explanations.
Independent scientists urge caution
Outside statisticians who reviewed the paper for the Science Media Centre noted the headline finding only narrowly cleared the conventional threshold for statistical significance, and that the large number of comparisons run across the dataset raises the chance some apparent effects arose by chance. They also pointed out the study measured markers of ovarian development rather than actual fertility or pregnancy outcomes later in life, leaving it unclear whether the infancy-stage differences will matter by adulthood.
Medical guidance has not changed as a result of the paper: paracetamol, known in the United States as acetaminophen and sold under brands including Tylenol, remains the recommended option for treating pain and fever during pregnancy, since untreated fever or severe pain can themselves pose risks to mother and fetus. The findings arrive against the backdrop of an already heated political debate over the drug's safety in pregnancy, after the Trump administration last year urged pregnant women to limit acetaminophen use over disputed claims linking it to autism, guidance that most obstetric groups said was not supported by the weight of evidence.
