Fetal Growth Restriction May Be Underestimated in Obese Patients

Abstract

INTRODUCTION: Fetal growth restriction is associated with poor perinatal outcomes. Unfortunately, only approximately 25% of children who are born growth restricted are identified prenatally. This underidentification of fetal growth restriction by standard measures is thought to be even higher in obese patients. The low sensitivity of outdated standardized fetal growth curves has been addressed by the development of customized fetal growth curves. Customized curves define fetal growth potential based on specific maternal factors. The objective of our study is to compare the identification of fetal growth restriction using customized compared with standardized curves (Hadlock) in normal-weight and obese patients. METHODS: In this retrospective study, 150 normal-weight (body mass index [BMI] less than 25 kg/m2) and 150 obese (BMI greater than 30 kg/m2) women aged 18–50 years who gave birth between July 1, 2008, and December 31, 2012, were included. Inclusion criteria were primiparity and an estimated fetal weight from a third-trimester ultrasound scan. For each fetus, a customized fetal growth curve was created using a program from www.gestation.net. Each fetus was then classified as growth-restricted or nongrowth-restricted using the third-trimester ultrasound-estimated weight and plotting it on the Hadlock and customized curves at the same gestational age. RESULTS: Obese women were more likely to have a fetus classified as growth-restricted by a customized curve compared with standard Hadlock's curve (odds ratio [OR] 2.1, 95% confidence interval [CI] 1.4–3.2, P=.001). Normal-weight women had no difference in classification of growth restriction (OR 0.9, 95% CI 0.7–1.2, P=.41). There was a statistically significant difference between the ORs comparing BMI categories (P=.001). CONCLUSION: In obese women, customized fetal growth curves better predict fetal growth restriction compared with standard growth curves.