Study question is fetal exposure to paracetamol associated with markers of ovarian function in infancy?

Summary answer Mild to moderate doses of prenatal paracetamol exposure, assessed by detailed maternal reports and urinary measurements, is associated with ovarian morphology and activity as well as reduced size of estrogen-responsive tissues in infant girls.

What is known already Maternal use of paracetamol is widespread. Across multiple independent animal studies, fetal exposure consistently impairs the formation of primordial ovarian follicles, causing subfertility and premature estropause in female offspring.

Study design, size, duration The Copenhagen Analgesic study (COPANA) is a single center, prospective, observational cohort study conducted at the Copenhagen University Hospital – Rigshospitalet, Denmark (March 2020 to November 2022).

COPANA cohort 3425 eligible participants. In total, 685 healthy, singleton pregnant women of Caucasian origin were enrolled in the first trimester of pregnancy, 302 girls examined at follow up. Exclusion criteria: maternal diabetes or thyroid disease, pre- or post-term delivery, or severe infant illness. Exposure: pregnant women reported paracetamol use biweekly and provided first-trimester urinary samples which were analyzed for paracetamol levels (LC-MS/MS) and adjusted for urinary osmolarity (n = 299). Girls were classified by timing of exposure: early fetal life (<17 weeks, n = 92), mid-late fetal life (≥17 weeks, n = 67), or unexposed controls (n = 143). A subgroup of girls was exposed exclusively in early fetal life (n = 22).

Independent confirmatory cohort 1210 girls followed from infancy to adolescence. Exposure: maternal self-reported any use of paracetamol during pregnancy reported in early third trimester (yes/no).

Main results and the role of chance Early fetal exposure was associated with reduced ovarian volume (−0.11 cm3, 95% CI −0.19 to −0.03) and uterine volume (−0.16 cm3, −0.32 to −0.01), whereas mid-late fetal exposure was associated with fewer ovarian follicles (−1.05, −1.71 to −0.39) compared to unexposed girls. AMH levels were lower in girls exposed exclusively in early fetal life (−0.45 SDS, −0.87 to −0.03) compared to unexposed girls. Maternal urinary paracetamol concentrations were inversely associated with ovarian and uterine volume as well as breast tissue diameter. In an independent cohort, fetal paracetamol exposure was associated with reduced uterine volume at puberty (−4.11 cm3, −7.29 to −0.92) and smaller ovarian volume in adolescence (−2.76 cm3, −4.82 to −0.70).

Limitations, reasons for caution The design of the study allows evaluation of exposure- outcome associations, while causality is strengthened by experimental models demonstrating comparable effects. Residual confounding by indication cannot be completely excluded, although results were robust after accounting for fever and other maternal factors. The analytic design of the current study limited our ability to evaluate whether frequency or patterns of paracetamol use influenced the observed associations.

Wider implications of the findings The consistency of findings across different assessment measures and cohorts, in combination with parallel evidence from animal studies, suggests potential long-term implications for female reproductive health.

Study funding/competing interest(s) This research was supported by Rigshospitalets Research Council under grant (E-22717-21), Læge Sofus Carl Emil Friis og hustru Doris Friis’ Legat (F-23936-01), Aase og Ejnar Danielsens Foundation (20-10-0367), Helsefonden (20-B-0388), Axel Muusfeldt Foundation (2020-0385) and The Danish Centre for Endocrine Disrupting Substances (CeHoS) (2022-23219). The authors have nothing to declare.

The authors have declared no competing interest.

This research was supported by Rigshospitalets Research Council under grant (E-22717-21), Laege Sofus Carl Emil Friis og hustru Doris Friis' Legat (F-23936-01), Aase og Ejnar Danielsens Foundation (20-10-0367), Helsefonden (20-B-0388), Axel Muusfeldt Foundation (2020-0385) and The Danish Centre for Endocrine Disrupting Substances (CeHoS) (2022-23219). The authors have nothing to declare.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The COPANA Study (ClinicalTrials.gov ID: NCT04369222) was approved by the ethical committee of the Capital Region of Denmark (H-19044036) and the Danish Data Protection Agency (P-2019-330). Participants gave written informed consent. For infant participants, consent was obtained from all adults with legal guardianship.

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