Objectives To compare the risk of adverse perinatal outcomes according to infants who are born small for gestational age (SGA; <10th centile) or large for gestational age (LGA; >90th centile), as defined by birthweight centiles that are non-customised (ie, standardised by sex and gestational age only) and customised (by sex, gestational age, maternal weight, height, parity, and ethnic group).
Design Comparative, population based, record linkage study with meta-analysis of results.
Setting Denmark, Finland, Norway, Wales, and England (city of Bradford), 1986-2019.
Participants 2 129 782 infants born at term in birth registries.
Main outcome measures Stillbirth, neonatal death, infant death, admission to neonatal intensive care unit, and low Apgar score (<7) at 5 minutes.
Results Relative to those infants born average for gestational age (AGA), both SGA and LGA births were at increased risk of all five outcomes, but observed relative risks were similar irrespective of wheth