Researchers report measurable changes in early female reproductive anatomy among infants whose mothers used Tylenol during pregnancy, but they emphasize the results do not prove the pain reliever is the cause and do not provide evidence about future fertility for the affected girls.
The study followed 302 three-month-old girls whose mothers’ acetaminophen use was tracked while pregnant. Investigators assessed exposure using urine samples collected from the women at regular intervals. Of the infants studied, 92 had first been exposed to acetaminophen before 17 weeks of gestation, 67 were first exposed after 17 weeks, and 143 were born to mothers who reported no use of the drug during pregnancy.
On average, those infants with prenatal exposure had smaller ovaries and uteruses, fewer ovarian follicles - the structures that contain immature eggs - and lower concentrations of reproductive hormones compared with infants whose mothers did not use acetaminophen, according to the paper published in Human Reproduction Open.
Study measurements and quantitative findings
The investigators reported that, overall, girls exposed in utero had a 40% smaller ovarian volume, a 13% smaller uterine volume and 23% fewer ovarian follicles compared with unexposed peers. Among babies exposed before 17 weeks, researchers also found lower levels of Anti-Müllerian hormone, a marker used to indicate the amount and quality of eggs in the ovaries.
None of the mothers in the study exceeded the recommended daily maximum dose of 4,000 milligrams of acetaminophen. Most reported taking the medication for common conditions such as headaches or musculoskeletal pain, and the doses were described as relatively low.
Secondary cohort and follow-up observations
To evaluate whether early findings might persist, the researchers also analyzed data from a separate cohort of 1,210 girls followed from infancy into adolescence whose mothers had reported acetaminophen use during pregnancy. In that group, fetal exposure was associated with smaller uterine size at puberty and smaller ovarian size during adolescence.
Study leaders cautioned that the research cannot predict outcomes for any single child. Many daughters of women who used acetaminophen during pregnancy had ovarian measurements similar to those of daughters born to women who did not use the drug, the researchers noted.
Context, interpretation and expert commentary
Investigators point out that a woman’s reproductive potential is established before birth: girls are born with the total complement of eggs they will ever have, and fetal development therefore determines the initial reserve. Animal studies previously had suggested fetal exposure to acetaminophen might affect the ovarian egg reserve and later reproductive function, but comparable human data had not been reported until now.
In a statement accompanying the paper, the study leader said the findings do not prove acetaminophen is the cause of the observed differences and that it is not possible from the current data to say whether the neonatal changes will translate into altered fertility or different timing of menopause later in life. The statement urged caution and recommended long-term follow-up extending into the reproductive years to determine potential implications.
In an editorial commentary, a reproductive medicine specialist noted the human findings are consistent with animal research and argued that long-term follow-up should extend into menopause. That commentator also suggested recommendations for acetaminophen use during pregnancy may need to be reassessed in light of the findings.
Guidance and public health considerations
Current medical guidelines continue to recommend acetaminophen as the standard option for treating pain and fever during pregnancy. Investigators reiterated that untreated high fever or severe pain can pose risks to both mother and fetus, and that the present study should not prompt immediate alarm among women who used acetaminophen while pregnant.
Separately, the article notes a public claim by a U.S. political figure linking prenatal acetaminophen use to autism; that assertion has been widely dismissed by the medical community and major health organizations as not supported by scientific evidence.
What remains unknown
Key questions remain unanswered. The study identifies anatomical and hormonal differences at early ages and associations at later developmental stages, but whether these translate into clinically meaningful changes in fertility, reproductive lifespan or age at menopause is not yet known and will require extended monitoring of the affected cohorts.
The researchers explicitly said the findings cannot be used to predict individual outcomes and encouraged long-term assessment to determine whether the early differences persist and what, if any, functional consequences they carry for reproductive health.
This analysis presents the study findings and expert perspectives while underscoring the need for follow-up research to clarify long-term effects.