Objective To compare the performance of estimated fetal weight (EFW) charts at the third trimester ultrasound for detecting small-and large-for-gestational age (SGA/LGA) newborns with adverse outcomes.Design Nationally representative observational study.Setting French maternity units in 2016.Population 9940 singleton live births with an ultrasound between 30 and 35 weeks of gestation. Methods We compared three prescriptive charts (INTERGROWTH-21st, World Health Organization (WHO), Eunice Kennedy Shriver National Institute of Child Health and Human Development [NICHD]), four descriptive charts (Hadlock, Fetal Medicine Foundation, two French charts) and a French customised growth model (Epop e).Main outcome measures SGA and LGA (birthweights <10th and >90th percentiles) associated with adverse outcomes (low Apgar score, delivery-room resuscitation, neonatal unit admission).Results 2.1% and 1.1% of infants had SGA and LGA and adverse outcomes, respectively. The sensitivity and specificity for detecting Conclusion Marked differences in the performance of descriptive as well as prescriptive EFW charts highlight the importance of evaluating them for their ability to detect high-risk fetuses.