Prenatal exposure to paracetamol is associated with smaller testicular volume: A COPANA cohort study of 287 healthy infant boys

Abstract STUDY QUESTION Is prenatal exposure to paracetamol associated with testicular function in male offspring? SUMMARY ANSWER Prenatal paracetamol exposure was associated with smaller testicular volume in infant boys. WHAT IS KNOWN ALREADY Paracetamol (also known as acetaminophen) is available over the counter and is frequently used by pregnant women. Animal studies and secondary analyses of mother-child cohorts suggest paracetamol can adversely affect testicular development. To our knowledge, this is the first cohort study primarily designed to test the association between prenatal paracetamol exposure and postnatal testicular function. STUDY DESIGN, SIZE, DURATION Prospective, observational pregnancy and birth cohort at a university hospital (2020–2022). Healthy, singleton pregnant women (n = 685) were enrolled during the first trimester, and 589 (287 boys) infants completed follow-up examination at 3 months of age. PARTICIPANTS/MATERIALS, SETTING, METHODS Data on maternal paracetamol use (yes/no and dose) were collected prospectively every two weeks throughout pregnancy. Based on the timing of fetal masculinization, participants were classified as exposed at any time during fetal life (n = 137), early exposure (gestational week (GW) ≤15; n = 81), late exposure (GW > 15; n = 118) or exposed during both early and late fetal life (n = 62). Unexposed boys served as controls (n = 150). The boys were examined at infancy (i.e., minipuberty at mean age 3.1 months ±0.3 SD). Predefined primary outcomes: anogenital distance (AGD), testicular volume and circulating levels of testosterone. MAIN RESULTS AND THE ROLE OF CHANCE Across exposure windows, prenatal paracetamol exposure was consistently associated with smaller testicular volume at 3 months of age. Effect estimates were largest in boys exposed at early as well as late fetal life; dose of paracetamol, median (interquartile range (IQR)) 8.5 g (4.0–16.6), testicular volume (β) −34.1 mm³, 95% CI − 65.5 to − 2.7, p = 0.033. LIMITATIONS, REASONS FOR CAUTION Residual confounding by indication cannot be excluded. The generalizability of the study may be affected by the homogeneity of the Copenhagen Analgesic Study (COPANA) cohort. Longitudinal follow-up is necessary for evaluation of reproductive health in adulthood. WIDER IMPLICATIONS OF THE FINDINGS In this prospective human cohort study, prenatal paracetamol exposure was associated with reduced testicular volume during minipuberty, a transient period of postnatal activation of the hypothalamic–pituitary–gonadal axis that is considered a critical window for assessing future reproductive function. FUNDING Rigshospitalet Research Council supports this work under grants (E-22778-02) and (E-22717-21). The research was furthermore funded by 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 fond (2020-0385) and The Danish Centre for Endocrine Disrupting Substances (CeHoS) (2022-23219). The publication was completed as part of the MERLON project (Svingen et al., 2024) under grant agreement No. 101137411. The MERLON project is funded by the European Union. Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Health and Digital Executive Agency (HADEA). Neither the European Union nor HADEA can be held responsible for them. DISCLOSURES DMK has received speaker fees from Merck. AJ has received speaker fees from Ipsen, Novo Nordisk, and Sandoz. AJ is Head of Department at a department that has received unrestricted research grants from Novo Nordisk and Lundbeck. All other authors declare no conflicts of interest. TRIAL REGISTRATION NUMBER The Copenhagen Analgesic Study (COPANA) (ClinicalTrials.gov NCT04369222).