Ultrasound Screening for Fetal Aneuploidy Using Soft Markers in the Overweight and Obese Gravida

Abstract

The risk of nearly all complications of pregnancy is increased by maternal obesity. Ultrasound examinations are routinely performed in pregnant women to evaluate fetal anatomy and screen for soft markers of aneuploidy. Ultrasound has shown that the most obese women are at the highest risk of fetal anomalies and aneuploidy. In a recent large trial, obese women who underwent second trimester ultrasound screening had higher false-negative rates and higher rates of missed than slender women diagnoses. Other than body mass index (BMI) ≥30, however, these data were not substratified by the degree of obesity, so the impact of the degree of obesity is unknown. This retrospective study was designed to determine the completion rate of ultrasound surveys among an obese population stratified by maternal BMI. A retrospective analysis was conducted of all ultrasound examinations performed at 18 to 24 weeks at a university referral center from 2004 to 2007. Ultrasound findings in obese and normal weight women were compared. The women were classified by their prepregnancy BMI as normal weight (BMI: 18.5-24.9 kg/m 2 ) or overweight (BMI: 25-29.9 kg/m 2 ), and as either obese class I (BMI: 30-34.9 kg/m 2 ), class II (BMI: 35-39.9 kg/m 2 ), or class III (BMI: ≥40 kg/m 2 ). A complete ultrasound examination was defined as satisfactory evaluation of at least 7 of the following 8 predetermined aneuploidy markers: short femur, short humerus, pyelectasis, thickened nuchal fold, echogenic bowel, choroid plexus cysts, 2 vessel cord, and intracardiac echogenic focus. A total of 8635 singleton women underwent 14,353 ultrasound examinations; 5690 patients were eligible for inclusion. Of these, 43.6% were normal weight, 29.2% were overweight and 27.1 % were obese. There was a significant difference in completion rates of ultrasound screening based on maternal BMI (normal weight: 64%, overweight: 64%, obese class I: 61%, obese class II: 55%, obese class III: 47%, P < 0.001). The incidence of an abnormal aneuploidy screen (presence of one of more markers) among all patients significantly decreased as the degree of obesity increased: normal weight 16%, overweight 13%, obese class I 15%, obese class II 12%, obese class III 10%, P < 0.02, but this appeared to be related to the ability to complete the scan; among patients in whom the scan could be completed, the incidence of abnormal screens was the same in all groups (P = 0.42). These findings show an inverse relationship between the completion rates for ultrasound aneuploidy screening and maternal BMI, indicating that obese women, especially those who are morbidly obese, are underscreened.