Association of Ultrasound Estimated Fetal Weight with Actual Birth Weight of Baby

Introduction: Fetal weight estimation is a precious tool for doctors to take informed decisions about timing & mode of delivery, and is also an independent risk factor for perinatal mortality. But there is conflicting evidence regarding accuracy of USG estimated fetal weight in literature. Our study was designed to find predictive ability of 3 rd trimester USG estimated fetal weight for the actual birth weight & its ability to predict LGA/SGA babies. Methods: A retrospective analytical study was conducted on 1280 patients after matching inclusion & exclusion criteria, from January 2016 to December 2020. Estimated fetal weight (EFW) was calculated on growth scan performed at 36 th /37 th week of gestation & it was compared with the actual birth weight of babies. The proportion of SGA, AGA & LGA babies was determined by plotting on INTERGROWTH -21 charts. Results: Study population was divided into 4 groups based on scan to delivery interval -Group A (≤ 1 week) (42.66%), B (1 -2 weeks) (30%), C (2 -3 weeks) (15.08%) & D (3 -4 weeks) (12.26%). There was no significant difference between EFW & actual birth weight in Group A (p=0.12); groups B, C, D had significant difference between EFW and newborn weight (p<0.001). This infers that EFW on USG can predict birth weight accurately if delivery occurred within 1 week of scan. The estimated percentages of SGA, AGA & LGA in the last growth scan & actual percentage of Low Birth Weight (LBW), Normal Weight & Big Babies at birth were significantly different overall (p<0.01). But, in group A (≤ 1 week scan to delivery interval), these were not significantly different (p=0.308), implying that growth scan, if the scan -delivery interval was within 1 week, was very effective in predicting the proportion of SGA & AGA babies. Conclusion: Ultrasound Estimated Fetal weight was accurate in predicting actual birth weight only when the scan -delivery interval is within 1 week. Also, last ultrasound done within 1 week of delivery, is able to predict SGA babies with significant accuracy, but not forLGA babies.