EP38.05: The accuracy of ultrasound estimated fetal weight at 41 weeks of gestation prior to induction of labour: prospective study

Abstract

To evaluate the accuracy of ultrasound estimated fetal weight (EFW) shortly before induction of labour in primiparous women induced by prologued gestation comparing accuracy of this measurement with third trimester ultrasound. Prospective study of 50 primiparous woman singleton pregnancies and cephalic presentation who were admitted to our unit for induction of labour due to prolonged gestation between April 2021 and December 2021. An ultrasound to estimated fetal weight 24h before induction was performed in all of them. Information of estimated fetal weight in third trimester was obtained from history records retrospectively. Both EFW were calculated using Hadlock formula and compared with birthweights. There was a high correlation between EFW at 41 weeks prior to labour induction and birthweight (R2 = 0.737, P < 0.001). EFW at third trimester ultrasound have not a good correlation with birthweight (R2 = 0.210, P > 0,143). The mean birthweight was 3469 ± 392 g. The mean EFW at 41 weeks was 4482 ± 414 g and mean absolute weight difference was −160 ± 293 g. The mean EFW in third trimester ultrasound was 2658 ± 262 g and mean absolute weight difference was 810 ± 423 g. Ultrasound EFW before induction of labour at 41 weeks is highly correlated with birthweight. Although, this trend used to overestimate fetal weight, their accuracy is superior than third trimester measurement. EFW should modified the way of delivery or monitorisation under labour (suspected fetal growth restriction), for that reason, we must look for the major accuracy.