The impact of reference growth standards on small- and large-for-gestational age outcomes among pregnancies conceived by fresh and frozen embryo transfers

Abstract

ObjectiveTo describe differences in the frequency of small-for-gestational-age(SGA) and large-for-gestational-age(LGA) driven by different birthweight curves in assisted-reproductive-technology(ART)-conceived pregnancies. DesignRetrospective cohort study SettingSingle academic medical center PatientsSingleton livebirths between 36+0-42+6 from fresh or frozen embryo transfer(ET) InterventionsNone Main Outcome MeasuresSGA (<10th percentile) and LGA (>90th percentile) classified by Fenton, INTERGROWTH-21, World Health Organization, Duryea, and Oken curves. ResultsMedian birthweight and gestational age at birth among fresh ET-pregnancies was 3289 (IQR 2977-3600)grams and 39.4 (IQR 38.6-40.3)weeks, respectively, and among frozen ET-pregnancies was 3399 (IQR 3065-3685)grams and 39.4 (IQR 38.7-40.1)weeks, respectively. The frequency of SGA neonates using each birthweight standard ranged from 5.8%-13.4% for fresh ET (p<0.001) and 3.5%-8.7% for frozen ET (p<0.001). LGA frequency ranged from 5.3%-14.3% for fresh ET (p<0.001) and 6.6%-21.2% for frozen ET (p<0.001). ConclusionsThe frequency of SGA and LGA neonates among ART-conceived gestations is partially driven by the birthweight standard. Selecting an appropriate standard that best reflects the patient population is critical to quantifying the risk of ART-conceived pregnancies.