Population versus customized fetal growth norms and adverse outcomes in an intrapartum cohort

Abstract

Objective: To compare population versus customized fetal growth norms in identifying neonates at risk for adverse outcomes (APO) associated with small for gestational age (SGA).

Study design: Secondary analysis of an intrapartum fetal pulse oximetry trial in nulliparous women at term. Birth weight percentiles were calculated using ethnicity- and gender-specific population norms and customized norms (Gardosi).

Results: Of the studied neonates, 508 (9.9%) and 584 (11.3%) were SGA by population (SGApop) and customized (SGAcust) norms, respectively. SGApop infants were significantly associated with a composite adverse neonatal outcome, neonatal intensive care admission, low fetal oxygen saturation, and reduced risk of cesarean delivery; both SGApop and SGAcust infants were associated with a 5-minute Apgar score < 4. The ability of customized and population birth weight percentiles in predicting APO was poor (12 of 14 APOs had area under the curve of <0.6).

Conclusion: In this intrapartum cohort, neither customized nor normalized population norms adequately identified neonates at risk of APO related to SGA.

Figure 1

distribution of neonates classified as small for gestational age (SGA) by the population (SGApop, n=508) and the customized methods (SGAcust, n=584). The diagram also shows the subgroups that are SGA by both methods (n=397) and SGA by population or customized norms only (SGApop only, n=111 and SGAcust only, n=187)

Figure 2

Odds and incidence of adverse perinatal and neonatal outcomes in SGA neonates by population or customized norms categories compared with those not SGA.