OP03.07: Single and serial fetal biometry to detect preterm and term small‐ and large‐for‐gestational age neonates: a prospective longitudinal study

To assess the value of single and serial fetal biometry for the prediction of small (SGA) and large for gestational age (LGA) neonates. Retrospective study including 3,440 pregnancies with at least two ultrasound (US) scans obtained at <36 weeks of gestation (17,334 scans). Primary outcomes were SGA (<5th) and LGA (>95th) at birth. Fetus-specific estimated fetal weight (EFW) trajectories were calculated by linear mixed-effects models using data up to a fixed gestational age (GA) cut-off (28, 32, or 36 weeks). Screen test positive for single biometry was based on Z-scores of the EFW at the last scan before each GA cut-off. Screen test positive for the longitudinal analysis was based on the projected EFW at 40 weeks from available measurements before each GA cut-off for each fetus. Single biometric screening based on the EFW at the last scan at <32 weeks had a sensitivity of 50% and 53% (FPR = 10%) in detecting preterm and term SGA and LGA neonates, respectively (AUC =82%). For the detection of LGA neonates using data up to the 32 and 36 weeks' GA cut-offs, single biometric analysis had a higher sensitivity than longitudinal analysis (52% vs 46% and 62% vs 52%, respectively; p < 0.05). Restricting the analysis to subjects with the last observation taken within 2 weeks from the GA cut-off, the sensitivity for the detection of LGA, but not SGA, neonates increased to 65% and 72% for a single biometry at the 32 and 36 weeks' GA cut-offs, respectively. SGA screening performance was higher for preterm (<37 weeks) than for term cases (73% vs 46%, p < 0.05) for a single biometry at <32 weeks. Longitudinal analysis of biometric parameters does not provide additional information when compared to the last measurement for predicting SGA and LGA neonates. Prediction of LGA neonates is improved if the US scans are performed as close as possible to the GA cut-off. The screening performance for SGA neonates is higher for neonates who will be delivered preterm.