Neonatal morbidity and small and large size for gestation: a comparison of birthweight centiles

Objective To compare rates of small- and large-for-gestational age (SGA and LGA) neonates using four different weight centiles, and to relate these classifications to neonatal morbidity. Study design Neonates born at 33-40 weeks' gestation in a multiethnic population were classified as SGA or LGA by population reference (Fenton), population standard (INTERGROWTH), fetal growth curves (WHO), and customized (GROW) centiles. Likelihood of composite morbidity was determined compared with a common appropriate-for-gestational age referent group. Result Among 45,505 neonates, SGA and LGA rates varied up to threefold by different centiles. Those most likely to develop neonatal morbidity were SGA or LGA on both the population reference and an alternative centile. Customized centiles identified over twice as many at-risk SGA neonates. Conclusions Customized centiles were most useful in identifying neonates at increased risk of morbidity, and those that were small on both customized and population reference centiles were at the highest risk.