Does transvaginal ultrasound at 13-15 weeks improve anatomic survey completion rates in obese gravidas?

Objective: Obesity increases the difficulty of completing the fetal anatomic survey. This is of added concern in obese gravidas who are at higher risk of congenital fetal anomalies. We hypothesized that incorporation of an early transvaginal assessment could improve the completion rate of the fetal anatomic survey in obese women.Methods: We performed a prospective, longitudinal, blinded study of obese gravidas (BMI ≥ 35 kg/m²) comparing the use of a single early second trimester transvaginal ultrasound in addition to midtrimester transabdominal ultrasound versus traditional serial midtrimester ultrasound alone for completion of the anatomic survey. Transvaginal ultrasound for anatomy was performed between 13 0/7 and 15 6/7 week followed by midtrimester anatomic ultrasound, with each patient serving as her own control. Structures were marked as optimally or suboptimally viewed after each ultrasound. Sonographers and reviewers were blinded to images from the transvaginal ultrasound. Completion rates and gestational age at completion were compared between groups.Results: Fifty subjects were included. Fetal anatomic survey was completed in 62% using standard midtrimester assessment versus 78% with the addition of early transvaginal assessment (p = .04). The survey was completed at an earlier gestational age utilizing the transvaginal approach (22 0/7 ± 6 3/7) compared to traditional midtrimester transabdominal ultrasound approach (25 2/7 ± 5 3/7) p < .0005.Conclusions: Incorporation of an early transvaginal assessment of anatomy in obese women improved the rate of completion and led to earlier gestational age at completion of the fetal anatomic survey. Consideration should be given to including an early transvaginal sonogram as part of routine assessment of women with a BMI ≥ 35.