Third Trimester Detection of Fetal Growth Abnormalities in Obese Pregnant Women: A Retrospective Cohort Study [31P]

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To determine if, in pregnant obese women, prenatal ultrasonography (US) can accurately predict abnormal birthweight (BW) in newborns.


We conducted a retrospective chart review of singleton deliveries of obese women between January 1, 2014 and March 31, 2015 at UVA. IUGR was defined as an EFW <10% while LGA was defined as EFW > 90%. BW was categorized into normal (2500-3999 grams), low (<2500 grams), and macrosomic (≥4000 grams). Chi squared tests and logistic regression were used for analyses.


We included 307 women in our study. Indicated third trimester growth US for chronic hypertension or diabetes occurred among 17.6% (54/307) of women. Among the remaining women without these indications, 70.4% (178/253) had at least one follow up US. Overall, 22.3% (44/197) of newborns had a discordant prenatal EFW and BW. For macrosomic infants, 13.9% (5/36) were LGA prenatally, while 58.33% (21/36) appeared normal. Among low BW (LBW) newborns, 13.2% (5/38) had IUGR prenatally, while 44.8% (17/38) had a normal EFW. Normal BW infants were rarely diagnosed as IUGR (1/232, 0.5%) or LGA (5/232, 2.2%). A BMI 35-40 (OR=0.41, 95%CI: 0.18-0.96), having 2-3 US (OR=0.31, 95%CI: 0.12-0.76), and diabetes (OR=0.41, 95%CI: 0.18-0.94) reduced the odds of predicting LBW and macrosomia.


In obese women, there is a high rate of discordance between prenatal fetal growth abnormalities and actual BW. Having a higher BMI or another comorbidity reduces the accuracy of predicting abnormal BW. Prenatal prediction of LBW or macrosomia does not improve after the first follow up growth US.

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