Infant size at birth is considered an important marker of the intrauterine environment. Accumulating epidemiologic evidence has shown associations of prenatal exposure to BPA to reduced infant birth weight. However, effects of BPA exposure before conception in either parent is unknown. Epidemiologic evidence on BPS - a BPA substitute - is practically absent. We examined associations between maternal and paternal preconception, as well as maternal prenatal urinary BPA and BPS concentrations and size at birth among 346 singletons born to couples from the Environment and Reproductive Health (EARTH) Study, an ongoing prospective preconception cohort of women and men seeking fertility evaluation in Boston, Massachusetts. Infant birth weight and head circumference were abstracted from delivery records. Mean preconception exposures were estimated by averaging urinary In-BPA and In-BPS concentrations in multiple maternal and paternal urine samples collected before pregnancy, and prenatal exposures estimated via multiple maternal pregnancy samples collected per trimester. Associations of urinary BPA and BPS concentrations with birth weight and head circumference were estimated using multivariable linear regression. Maternal preconception urinary BPA concentrations were inversely associated with birth weight and head circumference in adjusted models: each In-unit increase was associated with a decrease in birth weight of 119 grams (95%CI: -212, -27), and in head circumference of 0.60 centimeters (95%CI: -1.2, -0.03). Additional adjustment for gestational age or prenatal BPA exposure modestly attenuated results. Women with higher prenatal BPA concentrations had infants with lower mean birth weight (-75 grams, 95%CI: -153, 2). Paternal preconception urinary BPA concentrations were not associated with outcomes. No consistent patterns emerged for BPS exposure. This study suggests that the maternal preconception period may be a sensitive window for BPA effects on birth outcomes.
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