Improving Antenatal Prediction of Small‐for‐Gestational‐Age Neonates by Using Customized Versus Population‐Based Reference Standards

Objectives The purpose of this study was to evaluate whether the use of customized fetal reference standards improves the prenatal detection of intrauterine growth restriction. Methods We conducted a retrospective cohort study. Singleton pregnancies with a diagnosis of a small‐for‐gestational‐age (SGA) fetus based on the in utero reference standard of Hadlock et al (Am J Obstet Gynecol 1985; 151:333–337; Radiology 1991; 181:129–133) were identified from our ultrasound database, and customized percentiles were calculated by adjusting for maternal height, weight, ethnicity, parity, and sex. Results A total of 300 pregnancies were identified as SGA by both the Hadlock and customized standards, and 60 were identified as SGA by the Hadlock standard only. Small‐for‐gestational age pregnancies identified by the Hadlock standard only were significantly less likely to have any abnormal sonographic findings, including an elevated head to abdominal circumference ratio (8.3% versus 21.7%; P = .019), oligohydramnios (3.3% versus 13%; P = .027), abnormal umbilical artery Doppler findings (3.4% versus 14.7%; P = .017), maternal hypertensive disease (3.3% versus 12.7%; P = .041), and preterm delivery (6.7% versus 27.7%; P < .001). There was no difference in neonatal intensive care unit admission rates; however, neonates identified as SGA by the Hadlock standard only were less likely to have a postnatal diagnosis of SGA (9.1% versus 78.3%; P < .001) and had a shorter neonatal intensive care unit stay (median, 2 versus 8 days; P < .001). Conclusions Using a customized standard, we have identified a population of pregnancies with low rates of antenatal complications and sonographic findings associated with pathologic growth. Adoption of customized standards to improve our antenatal detection rate of intrauterine growth restriction may decrease the need for intervention in healthy but constitutionally small fetuses.