55 - First Trimester Anatomy Ultrasound for Obese Patients: a Randomized Controlled Trial

Women with BMI≥ 35 have incomplete anatomy ultrasounds (US) at 18-22 weeks more often than lean women, and need additional scans for missed structures. First trimester US is successful in lean women and for obese patients can bypass upper abdominal fat using the suprapubic crease or a transvaginal (TV) approach. This study compared completion rate of first trimester anatomy US to second trimester anatomy US, in women with BMI≥ 35.

Study Design:

This randomized controlled trial enrolled women with BMI≥ 35 carrying singletons and presenting before 14w0d. The primary outcome was completion rate (percent of US that imaged all structures in a protocol based on first trimester US literature) of US at 12w0d-13w6d, compared to completion rate of US at 18w0d-22w6d weeks (percent of US that imaged all structures in a protocol based on national guidelines). Also collected were completion rate of each structure, perinatal outcomes, and utility of a TV approach. A sample size of 128 was calculated based on completion rates of both techniques and the local loss to follow-up.

Results:

128 women were recruited, of whom 1 withdrew. 64 were randomized to first trimester US and 63 to second trimester US. 67% of first trimester US were complete compared to 53% of second trimester US (p=0.18). First trimester US plus second trimester US was more successful at completely imaging anatomy (76%) compared to second trimester US followed by additional scans for missing views (67%) in a probabilistic analysis for optimal management strategy. First trimester anatomy US was inferior in cardiac views such as the LVOT (48% vs 88%, p< 0.001) and vena cavae (53% vs 83%, p=0.001). No anomalies were missed during the study. A TV approach was necessary for 64% (28/59) of first trimester US, but all 30 first trimester US participants who responded to a survey rated their US “somewhat comfortable.”

Conclusion:

First trimester anatomy US provides earlier identification of fetal anatomy and earlier opportunity for counseling and confirmatory tests. A combination of first and second trimester US may form an optimal strategy in obese women.