BackgroundExposure to bisphenols may affect fetal growth and development. The trimester-specific effects of bisphenols on repeated measures of fetal growth remain unknown. Our objective was to assess the associations of maternal bisphenol urine concentrations with fetal growth measures and birth outcomes and identify potential critical exposure periods.MethodsIn a population-based prospective cohort study among 1379 pregnant women, we measured maternal bisphenol A, S and F urine concentrations in the first, second and third trimester. Fetal head circumference, length and weight were measured in the second and third trimester by ultrasound and at birth.ResultsAn interquartile range increase in maternal pregnancy-averaged bisphenol S concentrations was associated with larger fetal head circumference (difference 0.18 (95% confidence interval (CI) 0.01 to 0.34) standard deviation scores (SDS), p-value< 0.05) across pregnancy. When focusing on specific critical exposure periods, any detection of first trimester bisphenol S was associated with larger second and third trimester fetal head circumference (difference 0.15 (95% CI 0.05 to 0.26) and 0.12 (95% CI 0.02 to 0.23) SDS, respectively) and fetal weight (difference 0.12 (95% CI 0.02 to 0.22) and 0.16 (95% CI 0.06 to 0.26) SDS, respectively). The other bisphenols were not consistently associated with fetal growth outcomes. Any detection of bisphenol S and bisphenol F in first trimester was also associated with a lower risk of being born small size for gestational age (Odds Ratio 0.56 (95% CI 0.38 to 0.74) and 0.55 (95% CI 0.36 to 0.85), respectively). Bisphenols were not associated with risk of preterm birth.ConclusionsHigher maternal bisphenol S urine concentrations, especially in the first trimester, seem to be related with larger fetal head circumference, higher weight and a lower risk of being small size for gestational age at birth.