A standardized approach for the assessment of the lower uterine segment at first trimester by transvaginal ultrasound: a flash study.

Objectives: To evaluate the reproducibility of a standardized approach to lower uterine segment (LUS) imaging by transvaginal ultrasound at 11-14 weeks.

Methods: This was a "flash" study lasting for 1 month. Obstetrician-sonographers performing more than 50 first trimester ultrasounds per year participated. All consecutive women attending for their 11-14 weeks scan were included. A standardized, transvaginal approach to the imaging of LUS was defined. The sonographers recorded one or two images of the LUS. The quality of the images was assessed by sonographers and reviewed by an independent fetal medicine specialist using the same scoring system. Inter and intra-reviewer variability was assessed.

Results: Seventy-one sonographers and 851 pregnant women participated. The mean (±SD) and medium (IQR) scores attributed by sonographer versus reviewer were 5.01 (±0.92) and 5 [4-6] versus 4.68 (±1.14) and 5 [4-5.24], p = 0.08. The mean [95% CI] difference of -0.33 [-2.6;2] was recorded. There was good, moderate and poor agreement in 74.4%, 16.7% and 8.9% cases, respectively. Variability in inter-reviewer and intra-reviewer was low with the mean [95% CI] difference of -0.1 [-1.6;1.4] and -0.1 [-1.4;1.2] respectively.

Conclusions: A standardized approach to LUS imaging at 11-14 weeks is feasible and highly reproducible in a large population.