812 Comparing 32-week vs 36-week growth ultrasound for prediction of LGA infants in obese gravidae

Abstract

To compare 32 vs 36 week ultrasounds in prediction of large for gestational age (LGA) infants in a non-obese vs obese cohort. This was a retrospective cohort study from 01/01/18 to 01/01/19 of all growth ultrasounds performed from 30w0d to 32w6d and 35w0d to 36w6d in a single institution. Multifetal gestations and fetal demises were excluded. We determined the estimated fetal weight (EFW) for all patients using the Hadlock growth curve (GC). We defined suspected fetal macrosomia as EFW >90th percentile. LGA was defined as birthweight >90th percentile by the WHO and Fenton GCs, for term and preterm infants, respectively. Obesity was defined by a pre-pregnancy BMI of >=30 kg/m2. The primary outcome was the ability of the growth ultrasound to predict LGA in an obese cohort compared to a non-obese cohort. Predictive characteristics were calculated for each gestational age and the area under the receiver operating characteristic curve (AUC) were compared. A total of 885 women were included (n=760 32 week exams and n=324 36 week exams), 343 (38.76%) of which were obese. A total of 104 (11.75%) gravidae had infants that were LGA at birth. There were 100 gravidae (11.30%) who had a fetus measuring >90%ile at the 32 week ultrasound while 56 gravidae (6.33%) measured >90%ile at 36 weeks. No statistical differences were observed for the AUC for obese and non-obese gravidae at the 32 week (0.684 vs 0.662, p=0.658) (Figure 1) or 36 week (0.654 vs 0.600, p=0.228) growth ultrasounds (Figure 2). There was also no significant difference in the AUC between the 32 and 36 week growth ultrasounds (0.676 vs 0.628, p=0.093). No differences were observed for predicting LGA infants between obese and non-obese cohorts at either the 32 week or 36 week growth ultrasound.View Large Image Figure ViewerDownload Hi-res image Download (PPT)