First‐trimester and combined first‐ and second‐trimester prediction of small‐for‐gestational age and late fetal growth restriction

Objective To develop a first‐trimester or combined first‐ and second‐trimester screening algorithm for the prediction of small‐for‐gestational age (SGA) and late fetal growth restriction (FGR). Methods This was a retrospective study of women with singleton pregnancy, who underwent routine first‐, second‐ and third‐trimester ultrasound assessment. Late FGR was defined, at ≥ 32 weeks' gestation in the absence of congenital anomalies, as either (i) estimated fetal weight (EFW) or birth weight (BW) < 3 rd centile, or (ii) EFW < 10 th centile and either uterine artery mean pulsatility index (UtA‐PI) > 95 th centile or cerebroplacental ratio (CPR) < 5 th centile. Neonates with BW < 10 th centile, regardless of prenatal parameters, were defined as SGA. The predictive effectiveness of maternal and first‐ and second‐trimester factors was tested using logistic regression and receiver–operating characteristics curve analyses. Results A total of 3520 fetuses were included (late FGR, n  = 109 (3.1%); SGA, n  = 292 (8.3%)). Of the late FGR cases, 56 (1.6%) fulfilled the antenatal criteria (EFW < 3 rd centile or EFW < 10 th centile plus abnormal UtA‐PI or CPR) and were defined as prenatally detected late FGR. A first‐trimester screening model (comprising conception method, smoking status, maternal height, pregnancy‐associated plasma protein‐A (PAPP‐A) and UtA‐PI) could predict 50.0% of the prenatally diagnosed and 36.7% of the overall late FGR fetuses for a 10% false‐positive rate (FPR). A model combining first‐ and second‐trimester screening parameters (conception method, smoking status, PAPP‐A, second‐ trimester EFW, head circumference/abdominal circumference ratio and UtA‐PI) could predict 78.6% of the prenatally detected, and 59.6% of the overall late FGR fetuses, for a 10% FPR (area under the curve 0.901 (95% CI, 0.856–0.947) and 0.855 (95% CI, 0.818–0.891), respectively). The prediction of SGA was suboptimal for both first‐trimester and combined screening. Conclusions A simple model combining maternal and first‐ and second‐trimester predictors can detect 60% of fetuses that will develop late FGR, and 79% of those fetuses that will be classified prenatally as late FGR, for a 10% FPR. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.