Influence of chest/head circumference ratio at birth on obstetric and neonatal outcomes: The Japan environment and children's study

Objectives Some newborns that are not small‐for‐gestational‐age (non‐SGA, birthweight ≥10th percentile for a given gestational age) may have pathologic growth restrictions. This study examined the association of adverse obstetric and neonatal outcomes with chest/head circumference ratio at birth in non‐SGA and SGA newborns. Methods This study was a cross‐sectional evaluation of data from a nationwide prospective birth cohort study, the Japan Environment and Children's Study. We analyzed 93 690 non‐anomalous singletons born at 34–41 gestational weeks. We defined low, normal, and high chest/head circumference ratio as 90th percentile, respectively, according to the internally constructed chest/head circumference percentile chart. Modified Poisson regression was used to estimate adjusted prevalence ratios (aPR) for the outcomes studied. Results Compared with non‐SGA newborns with a normal ratio, those with a low ratio had an increased occurrence of low birthweight (1.75, 1.58–1.94 [aPR, 95% confidence interval]), cesarean delivery (1.34, 1.29–1.38), Apgar score