751 Longitudinal ultrasound versus gestation-adjusted projection of birth weight in pregnancies complicated by diabetes

Abstract

The aim of this study was to compare two methods of estimating fetal weight at delivery in women with diabetes in pregnancy; the longitudinal method and the gestation-adjusted prediction (GAP) of birthweight. We conducted a retrospective cohort study of all pregnancies complicated by either pregestational (PDM) or gestational diabetes (GDM) from 2010-2019 with delivery weight and serial third trimester sonographic data available for analysis. Ultrasound estimates were documented at two time points between 28 0/7-31 6/7 and 32 0/7-35 6/7 weeks’ gestation. Fetal weight at birth was predicted using the longitudinal and GAP methods (Figure 1). A Pearson correlation coefficient for each projection measure was calculated compared to birthweight. Test statistics were calculated for prediction of birth weight >4500g. Factors associated with under- and overestimation (±500g) of birthweight were investigated. 1,057 patients were included in the study. Relatively high correlation was seen for both methods (longitudinal: r=.818; p<.001, GAP: r=.812; p<.001). Both the absolute difference (p<.830) and absolute percent error (p=.758) were not different between methods (Table 1). Underestimation using the GAP method was more likely in PDM (61.8% vs 43.9%; p<.001), higher fetal abdominal circumference percentile (AC, 91% vs 77%; P<.001), and EFW percentile (71% vs 59%; p<.005). Neither AC nor EFW was significant with underestimation of longitudinal projection. For both measures’ overestimation was associated with higher EFW, higher AC, and greater gestational age at delivery. The longitudinal method had a higher sensitivity for birthweight >4500g (43.9% [28.5-60.3%] vs 31.7% [18.1-48.1%]). While the longitudinal and GAP methods have similar overall levels of agreement with birthweight. The longitudinal method may perform better in women with pregestational diabetes and in fetuses at higher extremes of weight with better prediction of birthweight >4500g.View Large Image Figure ViewerDownload Hi-res image Download (PPT)