Adjusting growth standards for fetal sex improves correlation of small babies with stillbirth and adverse perinatal outcomes: A state-wide population study

Abstract

Objectives Sex impacts birthweight, with male babies heavier on average. Birthweight charts are thus sex specific, but ultrasound fetal weights are often reported by sex neutral standards. We aimed to identify what proportion of infants would be re-classified as SGA if sex-specific charts were used, and if this had a measurable impact on perinatal outcomes. Methods Retrospective cohort study including all infants born in Victoria, Australia, from 2005–2015 (529,261 cases). We applied GROW centiles, either adjusted or not adjusted for fetal sex. We compared overall SGA populations, and the populations of males considered small by sex-specific charts only (SGAsex-only), and females considered small by sex-neutral charts only (SGAunadjust-only). Results Of those Conclusions Use of growth centiles not adjusted for fetal sex disproportionately classifies female infants as SGA, increasing their risk of unnecessary intervention, and fails to identify a cohort of male infants at increased risk of adverse outcomes, including stillbirth. Sex-specific charts may help inform decisions and improve outcomes.