531: Small for gestational age for the prediction of stillbirth: which growth chart should we use?

Abstract

Fetal growth restriction is a leading cause of stillbirth. However, the optimal growth chart that should be used to assess fetal growth and screen for fetal growth restriction remains unclear. The objective of the current study was to compare the performance of the commonly used growth charts in the prediction of stillbirth. A retrospective cohort study of all women with a singleton pregnancy who gave birth >24 weeks of gestation in a single center (2000-2016). The exposure of interest was small for gestational age (SGA), defined as birth weight < 10th percentile according 4 growth charts (Hadlock 1991, Intergrowth-21 (IG21), WHO 2017, and a Canadian birthweight-based reference (Kramer 2001)). The outcome of interest was stillbirth due to placental dysfunction or unknown etiology. Cases of fetal anomalies or stillbirth attributed to other etiologies were excluded. The association of SGA based on each of the 4 charts with primary outcome was determined using log binomial regression analysis. A total of 49,458 women were included in the cohort. There were 103 (0.21%) cases of stillbirth due to placental dysfunction or unknown etiology. The association of SGA with stillbirth was strongest when SGA was diagnosed using IG21 (RR 30.26, 95%-CI 20.27-45.17) and weakest for the Kramer chart (RR 10.38, 95%-CI 7.00-15.38) (Table). The detection rate of SGA for stillbirth was highest for Hadlock and WHO charts (63.1% and 61.2%, respectively), and lowest for IG21 and Kramer (52.4% and 48.5%, respectively) (Figure). The detection rate for preterm stillbirth was especially low for Karmer (54.3%) compared with Hadlock and WHO (70.4%, and 71.6%, respectively) (Figure). Although the diagnosis of SGA using IG21 has the strongest association with stillbirth, IG21 under detects SGA and stillbirth compared with the Hadlock and WHO charts. Clinician should be aware of the trade-off between these two statistical measures (association vs. detection rate) when choosing a growth chart to screen for SGA.View Large Image Figure ViewerDownload Hi-res image Download (PPT)