The purpose of this study was to assess the impact of the free choice of ultrasound propagation velocity on ultrasound image construction to improve the completion rate and anatomical quality of fetal second-trimester ultrasound examination in obese women.

This repeated cross-sectional single-center study retrospectively collected second-trimester ultrasound images of 88 obese women. During the first period, ultrasound examinations were performed in 44 women (mean age, 31.4±5.9 [SD] years; range: 21.1 - 45.3 years) applying only the standard 1540m/s tissue ultrasound velocity (group 1). During the second period, ultrasound examinations were performed in other 44 women (mean age, 31.4±5.1 [SD] years; range: 20.6 - 41.6 years) with the operator free to choose among three available velocity settings (1420m/s, 1480m/s or 1540m/s) for the scanning planes for the morphological images (group 2). All women underwent mid-trimester ultrasound examination at 20 to 24 gestational weeks. Two observers assessed the examinations in both groups for completeness, quality, and duration of fetal ultrasound examinations.

No differences in age (P>0.99), body mass index (P=0.67), prevalence of previous cesarean delivery (P=0.30) or gestational age at the second-trimester scan (P=0.20) were found between the two groups. The mean cumulative duration of these ultrasound examinations was longer in group 1 than in group 2 (for both the complete (P=0.04) and incomplete (P=0.03) examinations). The quality of the anatomic images according to Salomon's criteria was less often acceptable in group 1 (5/44, 11.4%) than in group 2 (15/44, 34.1%) (P=0.02).

Free choice of ultrasound velocity improves the overall performance of fetal second-trimester ultrasound examinations in obese women.