448: The effect of morbid obesity on estimation of fetal weight by ultrasound

Abstract

Although the accuracy of estimated fetal weight by ultrasound in overweight and obese women has been verified in prior studies, many of them were performed 10 or more years ago. Since then obesity rates in the US have dramatically increased and ultrasound technology continues to improve. Thus is it important to determine if morbid obesity decreases the accuracy of the estimation of fetal weight by ultrasound in the modern patient population. After obtaining IRB approval, a clinical database of patients that had fetal ultrasounds at Wake Forest Baptist Medical Center and delivering at Forsyth Medical Center between 2010 and 2017 was searched to identify patients delivering after 24 weeks that had an ultrasound assessment of fetal weight within 10 days of delivery. These patients were stratified into 3 groups based on body mass index (BMI): 1) normal weight (BMI <25), 2) overweight & obese (BMI 25-39), and 3) morbidly obese (BMI≥40). The difference in grams between estimated fetal weight by ultrasound and birth weight were compared between groups using a one-way ANOVA. There were 92 women in the normal weight group, 230 in the overweight & obese group, and 217 women in the morbidly obese group. The difference between the ultrasound estimated fetal weight and birth weight was 265±247 g, 207±181 g, and 217±191 g, respectively. No significant differences were noted between the groups. Although ultrasound resolution is known to be poor in women who are overweight or obese, the accuracy of the estimation of fetal weight is not affected by maternal size even in morbidly obese patients. Thus, ultrasound estimations of fetal weight in morbidly obese women can be relied upon when making clinical decisions.