Customized versus population fetal growth norms and adverse outcomes associated with small for gestational age infants in a high-risk cohort

Objective To compare population versus customized fetal growth norms in identifying neonates at risk for adverse perinatal and neonatal outcomes (AOs) associated with small for gestational age (SGA) in high-risk women. Design Secondary analysis to a multicenter treatment trial of pregnant women at high risk for preeclampsia using low-dose aspirin versus placebo. The associations between SGA by population (SGApop) and customized (SGAcust) norms and AOs were evaluated. Results A total of 2,289 mother/infant pairs were included in the analysis. The rates of SGA in the aspirin and placebo groups were similar by the customized (22.8% vs 23.9%; p=0.55) or population (8.7% vs 7.5%; p=0.54) norms; however, they were lower using population norms compared with customized norms (p<0.001). SGAcust, but not SGApop, was associated with spontaneous preterm birth (odds ratio [OR]: 1.44, 95% confidence interval [CI]: 1.15-1.81; p<0.001), preterm premature rupture of membranes (OR 1.42 95% CI 1.05-1.92; p=0.02), and cesarean delivery (OR: 1.35, 95% CI: 1.11-1.64; p=0.002). Both SGAcust and SGApop were associated with the composite neonatal outcome, indicated preterm delivery before 32, 35, and 37 weeks, oligohydramnios, fetal distress, as well as decreased risk of oxygen requirement. Neither was associated with preeclampsia. Conclusion Customized approach for assessment of fetal growth was associated with higher SGA rates and better identification of SGA neonates at risk for AOs.