Prenatal acetaminophen exposure associated with reduced ovarian and uterine size in infant girls, study finds
Researchers observed that babies whose mothers used acetaminophen during pregnancy had smaller ovaries, fewer follicles and smaller uteruses, though the study does not establish causality or predict future fertility.
A study of 302 three-month-old girls found that prenatal exposure to acetaminophen (Tylenol) was linked to reduced ovarian volume, fewer ovarian follicles and smaller uterine size, as well as lower levels of reproductive hormones. The infants whose mothers reported using the medication before 17 weeks of gestation showed the most pronounced differences.
The research, published in Human Reproduction Open, compared three groups: 92 infants exposed early in pregnancy, 67 exposed later, and 143 whose mothers did not use acetaminophen. Mothers provided urine samples throughout pregnancy, and none exceeded the recommended daily maximum dose of 4,000 mg. Most used the drug for headaches or musculoskeletal pain.
"Women who used acetaminophen during pregnancy should not be alarmed by the findings," study leader Margit Bistrup Fischer of Rigshospitalet in Copenhagen said in a statement.
The investigators also examined a separate cohort of 1,210 girls followed from infancy to adolescence. In that group, fetal exposure correlated with smaller uteruses at puberty and smaller ovaries during teenage years. However, Fischer emphasized that the study does not prove the medication caused the changes and cannot predict individual outcomes.
Current medical guidelines continue to consider acetaminophen safe for treating pain and fever in pregnancy, noting that untreated high fever or severe pain can pose risks to both mother and fetus. Some experts, such as reproductive-medicine specialist Christian De Geyter, suggest that the findings merit longer-term follow-up into menopause and a re-evaluation of usage recommendations.