RCOG versus ACOG: Whose method is better for diagnosing fetal growth restriction?

The Royal College of Obstetricians and Gynaecologists (RCOG) endorses the use of “EFW <10th or Abdominal circumference (AC) <5th percentile” to diagnose fetal growth restriction (FGR), whereas the American College of Obstetricians and Gynecologists (ACOG) endorses the use of EFW <10th percentile alone. We set out to determine which method predicts small-for-gestational age (SGA) at birth most effectively. We performed a review of deliveries at our institution from January 1, 2013 to March 31, 2017. Singleton, non-anomalous and well-dated fetuses with an ultrasound (US) exam within 30 days of delivery were included. EFWs were calculated and percentiles assigned using the Hadlock intrauterine growth curve. Birth weight percentiles were assigned using the sex-specific curve published by Olsen et al, and SGA was defined as birth weight <10th percentile. We calculated the sensitivity, specificity, positive and negative predictive values for various approaches using AC and EFW to diagnose fetal growth restriction (FGR), including the methods endorsed by ACOG and RCOG. The true positive rates were plotted graphically as a function of the false positive rates for each diagnostic approach to demonstrate receiver-operator characteristics and determine which approach had the best balance of true and false positives. We identified 1704 consecutive pregnancies that had an US within 30 days of delivery, with a mean US-delivery interval of 14.0 days (SD 8.6). There were 235 SGA neonates (13.8%). Compared to EFW alone, using either EFW <10th or AC <5th percentile to diagnose FGR correctly predicted 8 additional cases and added 13 false positives. The sensitivities and specificities of the various methods were similar, as were the receiver-operator characteristics. Adopting “EFW or AC <10th percentile” instead of EFW alone to diagnose FGR identified an additional 17 cases of SGA while leading to 40 additional false positives, a ratio of 2.4 false positives for each true positive, whereas the approach of “EFW <10th or AC <5th percentile” generated only 1.6 false positives for each added true positive. While the diagnostic approaches for FGR endorsed by RCOG and ACOG performed comparably to predict SGA at birth, the RCOG method identified a small number of additional cases while adding an acceptable number of false positives.View Large Image Figure ViewerDownload Hi-res image Download (PPT)