Many factors—including environmental pollutants, nutritional factors, and infectious agents—begin to influence children’s health as early as the prenatal and perinatal periods. The Elfe cohort (French Longitudinal Study from Childhood) will analyze these exposures and assess their impact on the health of 20,000 children born in 2011 and followed through adulthood. A pilot study, conducted in October 2007 on more than 500 births, showed an 80% success rate for biological sample collection in maternity wards. This study enabled the testing of collection procedures to derive scientific insights for scaling the study to the national level, particularly for the measurement of emerging pollutants such as bisphenol A (BPA) or phthalates. Phthalates and BPA are endocrine disruptors that can affect development and reproduction. This pilot study provides an initial estimate of maternal exposure to these substances in maternity wards across two French regions. Median urinary concentrations of BPA, MEHP, and its metabolites (5-OH-MEHP and 5-oxo-MEHP) are similar to those found in other studies, but the elevated concentrations and differences observed depending on the type of delivery suggest specific exposure in the maternity ward. The hypothesis raised is that of contamination via medical equipment. These results should be taken into account when designing biomonitoring studies in this population. They also highlight a route of exposure, via medical devices, for pregnant women and their newborns during prolonged hospital stays (in neonatal intensive care units or gynecology-obstetrics units). (R.A.)