A new study published in Human Reproduction Open has found that female infants exposed to acetaminophen (Tylenol) in the womb may have smaller ovaries, fewer ovarian follicles, and smaller uteruses compared to unexposed infants. The research, led by Margit Bistrup Fischer at Rigshospitalet in Copenhagen, examined 302 three-month-old girls whose mothers’ prenatal acetaminophen use was tracked throughout pregnancy. The study did not establish a causal link but noted these differences could have implications for future fertility.
The findings align with prior animal research suggesting that fetal exposure to acetaminophen might affect ovarian development. However, the researchers emphasized that long-term follow-up is needed to determine whether these early physical variations translate to fertility challenges later in life or earlier menopause. Fischer stated that pregnant women who have used the drug should not be alarmed, as the study only identified associations at a population level and cannot predict outcomes for individual children.
Separate research, based on decades of health records from over 220,000 children, found no link between prenatal acetaminophen use and increased risks of autism or ADHD. The analysis, covering data from more than 120,000 children, concluded that acetaminophen remains the only recommended over-the-counter pain reliever for pregnant women when alternatives like ibuprofen pose higher risks of birth defects. The studies were published amid ongoing debates over acetaminophen’s safety during pregnancy.
Key Findings on Fertility Markers
The Danish study measured reproductive organ development in infants whose mothers took acetaminophen during pregnancy. Among the findings:
- Smaller ovaries in exposed infants.
- Fewer ovarian follicles, which contain immature eggs.
- Smaller uteruses and lower levels of reproductive hormones.
The research team noted that these differences were observed regardless of when during pregnancy the drug was taken, though the study focused on exposure during the first two trimesters.
Autism and ADHD Risk Findings
A separate analysis of health records from over 220,000 children found no association between maternal acetaminophen use and diagnoses of autism or ADHD. The study, which reviewed data spanning two decades, contradicts previous claims that the drug might increase neurodevelopmental risks. Researchers warned that avoiding acetaminophen for fever or pain could lead to unsafe alternatives or complications such as preterm labor or miscarriage.
Expert Reactions and Recommendations
Fischer and other experts stressed that the fertility-related findings are preliminary and require further study. They advised pregnant women to consult their doctors before making changes to medication use. The U.S. Food and Drug Administration (FDA) currently lists acetaminophen as safe for use during pregnancy when taken as directed, though it recommends using the lowest effective dose for the shortest duration possible.
The conflicting findings underscore the complexity of balancing medication safety during pregnancy. While acetaminophen remains the standard recommendation for pain and fever relief, ongoing research continues to explore potential long-term effects on fetal development.