Reply.

Abstract

We thank Prof. Lees et al. for their comments regarding our study1 in which we endeavored to apply the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG)2 and Society for Maternal–Fetal Medicine (SMFM)3 definitions of fetal growth restriction (FGR) to a pre-existing cohort of patients with the aim to compare their performance in predicting neonatal small-for-gestational age (SGA) and composite adverse neonatal outcome. As outlined in the Discussion, our study has limitations. In table S1 of the study, we report that six of the 53 fetuses with late-onset FGR according to the ISUOG definition had estimated fetal weight (EFW) or fetal abdominal circumference (AC) crossing centiles of more than 2 quartiles on growth centiles. Our group has previously compared the ability of the Delphi criteria for FGR (including AC or EFW crossing > 2 quartiles) with that of EFW < 10th percentile for gestational age to predict neonatal SGA, and did not find the Delphi criteria to be a better predictor4. Furthermore, other studies have shown that the addition of fetal growth velocity between 20 and 36 weeks' gestation does not improve the ability of EFW at 35–37 weeks to predict delivery of a SGA neonate5. Lees et al. also questioned the utilization of neonatal SGA as a proxy for FGR. We agree with the authors that most fetuses with EFW or AC < 10th percentile but > 3rd percentile for gestational age and normal fetal surveillance (umbilical artery Doppler, non-stress test or biophysical profile) are less likely to have poor perinatal outcome. However, the optimal way to incorporate Doppler evaluation of the middle cerebral artery, uterine artery and ductus venosus, or the cerebroplacental ratio, in the management of early- and late-onset FGR is not yet clear6-8. We also agree that labeling more fetuses as being growth restricted may not reflect an increase in the detection of those fetuses that truly have placental pathology and would benefit from early intervention. Nevertheless, in our study, we aimed to compare the performance of the different diagnostic criteria for FGR of the two leading governing bodies in fetal medicine. Lastly, we agree that the prediction of adverse outcome in FGR pregnancies, especially those with late-onset FGR, is poor by both definitions of FGR. Unfortunately, the optimal definition and management protocol for FGR remains elusive and we acknowledge that some of the guidelines developed by both the SMFM and ISUOG for the diagnosis and management of FGR are not supported by high-level evidence. However, the simplicity of the SMFM diagnostic criteria, which are based on only AC and/or EFW, makes easier their implementation across the globe.