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By Daniella Gray
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Scientists tracking children's development from infancy into adolescence noticed a surprising trend among some girls in their study.
The clue pointed back to something their mothers had taken during pregnancy.
Researchers in Denmark found that girls exposed to paracetamol (Tylenol) in the womb showed differences in several markers linked to ovarian development, from infancy through adolescence.
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The findings do not prove the drug caused the changes, but the researchers say they add to growing evidence from animal studies that fetal exposure may have lasting effects on female reproductive health.
Lead author Dr. Margit Bistrup Fischer, a post-doctoral researcher in the Department of Growth and Reproduction at Rigshospitalet in Copenhagen, stressed that the findings should not prompt pregnant women who need paracetamol to stop taking it.
“However, it does contribute to a growing signal that we should pay closer attention to use during pregnancy, especially because paracetamol is an over-the-counter medicine that is often perceived as entirely risk-free,” Fischer told Newsweek.
The study, published in Human Reproduction Open, followed 302 girls from a prospective Danish pregnancy cohort and examined markers of reproductive development during infancy.
Researchers tracked mothers' paracetamol use throughout pregnancy using detailed questionnaires and urine samples.
The team found that daughters exposed to paracetamol during pregnancy tended to have smaller ovaries and uteruses, along with differences in ovarian activity.
Girls exposed during early pregnancy had reduced ovarian volume and smaller uterine volume compared with unexposed children, while exposure later in pregnancy was associated with fewer ovarian follicles, the structures that contain immature eggs.
Researchers also observed lower levels of anti-Müllerian hormone (AMH) among some girls exposed early in pregnancy.
In adults, AMH is often used as a marker of ovarian reserve, though the significance of differences seen in infancy is not yet clear.
To see whether the findings persisted, the researchers examined an independent cohort of 1,210 girls who had been followed from infancy into adolescence.
There, they found similar patterns. Prenatal exposure to paracetamol was associated with smaller uterine volume at puberty and reduced ovarian volume during adolescence.
Paracetamol use during pregnancy is widespread, with the researchers noting that more than half of pregnant women use the medication.
Previous studies in rodents have suggested fetal exposure can reduce ovarian follicle reserves and shorten reproductive lifespan, prompting scientists to examine whether similar effects could be seen in humans.
Whether the differences seen in childhood ultimately affect fertility is still a major question which remains unanswered.
“We observed differences in markers of ovarian function, but we do not yet know whether these changes translate into clinically meaningful effects on fertility later in life,” Fischer said. “For this we need larger studies with longer follow-up.”
Dr. Lucy Hooper, a private general practitioner and co-founder of Coyne Medical, who was not linked to the study, pointed out that the researchers measured markers linked to ovarian development, such as ovarian size and hormone levels, rather than long-term reproductive outcomes.
As a result, it remains unclear whether the differences observed in infancy will have any meaningful impact on puberty, ovarian reserve or fertility later in life.
"It’s really important to notice that when they narrowed the analysis down to babies who had been exposed only in early fetal life, so before 17 weeks of pregnancy, that was actually a very small subgroup of just 22 babies," Hooper told Newsweek.
Hooper noted that some of the differences seen in the study were relatively small and not measured very precisely, meaning the findings should be interpreted with caution.
She added that pregnant women should continue following current medical advice: using the lowest effective dose of paracetamol for the shortest possible time when needed.
Fischer said the study does not necessarily call for changes to existing medical advice, but it may encourage closer consideration of when the drug is used.
“Whether the overall evidence base is now strong enough to warrant changes to recommendations is ultimately a matter for regulatory authorities and clinical guideline groups to assess,” she said.
She noted that many women in the study used paracetamol for reasons other than fever or severe pain, situations where measures such as rest, hydration, physiotherapy, exercise, heat treatment or other supportive approaches may sometimes be sufficient.
“Ultimately, the decision should be based on an individual's symptoms and made in consultation with a healthcare professional when needed,” Fischer said.
Reference
Margit B Fischer, Gylli Mola, Karin Sundberg, Lone Scheel, Katrine B Wraae, Ane L Rom, Hanne Frederiksen, Richard A Anderson, Maria Assens, Anna-Maria Andersson, Lærke Priskorn, Jørgen H Petersen, Hanne K Hegaard, Katharina M Main, David M Kristensen, Anders Juul, Casper P Hagen, Fetal exposure to paracetamol is associated with altered markers of ovarian development and reduced uterine volume in girls: the COPANA study, Human Reproduction Open, Volume 2026, Issue 3, 2026, hoag073, https://doi.org/10.1093/hropen/hoag073
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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