Redefining fetal growth restriction using gastroschisis-specific growth curves.

INTRODUCTION: Fetal growth restriction (FGR) occurs in a significant proportion of pregnancies complicated by gastroschisis. Due to abdominal organ herniation, fetal abdominal circumference often measures less than expected when using Hadlock biometric measurements derived from non-anomalous fetuses. Therefore, growth restriction may be overdiagnosed in fetuses with gastroschisis. Our objectives were (1) to create second- and third-trimester fetal growth curves (nomograms) specific to gastroschisis and (2) to evaluate antenatal and delivery outcomes for fetuses diagnosed with fetal growth restriction by non-anomalous Hadlock growth curves compared to gastroschisis-specific nomograms. METHODS: This was a single-institution, retrospective cohort study of pregnancies complicated by isolated gastroschisis who delivered between 2011 and 2020. Using ultrasound biometric data, we generated growth curves specific to fetuses with gastroschisis, defining the 10th, 50th, and 90th percentiles between 15 and 37 weeks' gestation. To utilize the same formula most commonly incorporated into ultrasound software programs, estimated fetal weight in grams was calculated using the Hadlock formula. This generated new anomaly-specific nomograms and percentiles based on gastroschisis-specific biometric data. We compared antepartum and delivery outcomes for fetuses diagnosed with FGR by non-anomalous Hadlock growth curves to those diagnosed with FGR by gastroschisis nomograms using a non-parametric model and ANOVA chi-square. Perinatal outcomes were analyzed with t-test, chi-square, or Fisher's exact test. RESULTS: Five biometric nomograms were generated for gastroschisis fetuses, including estimated fetal weight, biparietal diameter, head circumference, abdominal circumference, and femur length. Estimated fetal weight curves for gastroschisis fetuses were downshifted significantly compared to 1984 Hadlock growth curves (p < 0.001). The gastroschisis-specific 50th percentile curve virtually overlays the non-anomalous Hadlock 10th percentile curve for estimated fetal weight, with similar findings for abdominal circumference and femur length. Based on the revised growth curve, 60% of gastroschisis fetuses diagnosed with FGR by non-anomalous Hadlock did not meet criteria for FGR by gastroschisis-specific nomograms. When comparing fetuses diagnosed with FGR by the revised gastroschisis curve compared to non-anomalous Hadlock, the new gastroschisis-specific curve was more strongly associated with 6 out of 19 clinically relevant outcomes, including: betamethasone administration (52% vs. 45%, p < 0.001), abnormal umbilical artery Doppler measurement (56% vs. 42%, p = 0.008), admission or induction prior to spontaneous labor (96% vs. 82%, p < 0.001), worsening bowel findings as the indication for delivery (39% vs. 28%, p = 0.03), increased cesarean delivery (54% vs. 49%, p = 0.001), and decreased vaginal delivery (46% vs. 51%, p = 0.001). CONCLUSION: Fetuses with gastroschisis have a growth curve that is distinctly different from that defined by the non-anomalous Hadlock curve. The 1984 Hadlock curves potentially overdiagnose FGR compared to gastroschisis-specific curves. FGR defined by gastroschisis-specific growth curves is strongly associated with many of the common perinatal outcomes seen in pregnancies complicated by this anomaly. Given the known risks of prematurity as well as the financial and labor costs of intensive antenatal surveillance, using gastroschisis-specific growth curves may assist in improved risk stratification and delivery planning among cases of gastroschisis.