Prediction of small-for-gestational-age neonates at 35-37 weeks' gestation: contribution of maternal factors and growth velocity between 20 and 36 weeks

Objectives To evaluate the performance of ultrasonographic estimated fetal weight (EFW) at 35+0 to 36+6weeks' gestation in the prediction of delivery of a small-for-gestational-age (SGA) neonate and assess the additive value of, first, maternal risk factors and, second, fetal growth velocity between 20 and 36weeks' gestation in improving such prediction. Methods This was a prospective study of 44 043 singleton pregnancies undergoing routine ultrasound examination at 19+0 to 23+6 and at 35+0 to 36+6weeks' gestation. Multivariable logistic regression analysis was used to determine whether addition of maternal risk factors and growth velocity, the latter defined as the difference in EFW Z-score or fetal abdominal circumference (AC) Z-score between the third-and second-trimester scans divided by the time interval between the scans, improved the performance of EFW Z-score at 35+0 to 36+6weeks in the prediction of delivery of a SGA neonate with birth weight < 10th and < 3rd percentiles within 2 weeks and at any stage after assessment. Results Screening by EFW Z-score at 35+0 to 36+6weeks' gestation predicted 63.4% (95% CI, 62.0-64.7%) of neonates with birth weight < 10th percentile and 74.2% (95% CI, 72.2-76.1%) of neonates with birth weight < 3rd percentile born at any stage after assessment, at a screen-positive rate of 10%. The respective values for SGA neonates born within 2 weeks after assessment were 76.8% (95% CI, 74.4-79.0%) and 81.3% (95% CI, 78.2-84.0%). For a desired 90% detection rate of SGA neonate delivered at any stage after assessment, the necessary screen-positive rate would be 33.7% for SGA< 10th percentile and 24.4% for SGA< 3rd percentile. Multivariable logistic regression analysis demonstrated that, in the prediction of a SGA neonate with birth weight < 10th and < 3rd percentiles, there was a significant contribution from EFW Z-score at 35+0 to 36+6weeks' gestation, maternal risk factors and AC growth velocity, but not EFW growth velocity. However, the area under the receiver-operating characteristics curve for prediction of delivery of a SGA neonate by screening with maternal risk factors and EFW Z-score was not improved by addition of AC growth velocity. Conclusion Screening for SGA neonates by EFW at 35+0 to 36+6weeks' gestation and use of the 10th percentile as the cut-off predicts 63% of affected neonates. Prediction of 90% of SGA neonates necessitates classification of about 35% of the population as being screen positive. The predictive performance of EFW is not improved by addition of estimated growth velocity between the second and third trimesters of pregnancy. Copyright (c) 2019 ISUOG. Published by John Wiley & Sons Ltd.