A Learning Curve for First-Trimester Anatomy Ultrasound in Obese Patients

Objectives: A recent randomized controlled trial of first-trimester anatomy ultrasound in obese women found some advantages to using this technique in this population, but some aspects of feasibility were not clear, such as whether first-trimester ultrasound can be brought outside of a research setting. The learning curve for first-trimester anatomy has been described in the general population, but a learning curve has not been described for this technique in obese patients. This study sought to describe a learning curve for first-trimester anatomy ultrasounds in obese patients with an operator familiar with the basics of first-trimester imaging. Design: This was a secondary analysis of the EASE-O pilot randomized controlled trial (NCT04639973), which recruited 128 women with a BMI >= 35 kg/m2 and randomized them into two groups based on the timing of the first evaluation of fetal anatomy, to compare the completion rate of first- and second-trimester anatomy ultrasound. Participants: Pregnant women with a BMI >= 35 kg/m2 participated in the study. Setting: Between January 2021 and February 2022, the study was conducted at maternal-fetal medicine clinics in Houston, TX, USA. Methods: This secondary analysis evaluated data on the completion rate of first-trimester scans from the parent trial. Scans were grouped into bin sizes of 3, and prop_model for R version 4.2.0 for Windows was used to generate a learning curve across the first 60 scans. Results: The parent study included 60 scans performed by one imager who had previously only done first-trimester scans in lean patients for limited anatomy. The probability of a complete scan increased over 60 scans from 0.38 to 0.69; 29 scans were required to reach the final probability, after which only marginal improvement followed. Limitations: The major limitation is the inclusion of only one operator for this curve. Conclusions: For an ultrasound operator with basic familiarity in first-trimester imaging, approximately 30 scans are needed to acquire a completion rate of 70% for detailed first-trimester anatomy in women with BMI >= 35 kg/m2. This can be used in education and training programs focused on imaging in the first trimester.