Visualization of the Fetal Corpus Callosum in Routine Second Trimester Screening Ultrasound Examinations.

Objectives: The primary aim of this study was to determine the visualization rate of the corpus callosum (CC) in the mid-sagittal plane of ultrasound examinations performed between 18 and 22 weeks' gestation. The secondary aims were to compare this rate to that achieved 5 years earlier at the same center; assess the need for transvaginal ultrasound; identify fetal head positions most favorable for sagittal CC assessment; and evaluate the impact of maternal body mass index (BMI) and gestational age on CC visualization.

Methods: A retrospective analysis of images from second trimester screening examinations of singleton pregnancies performed between January 2019 and June 2019 was undertaken. The mid-sagittal image of the CC was scored on a scale from 0 to 4, with one point assigned for the visualization of each anatomical part. A score of 4 indicated complete visualization, a score of 1 to 3 was considered partial visualization, and a score of 0 represented nonvisualization. The chi-squared test was used to compare the visualization rates to those achieved 5 years earlier and previously reported by our group.

Results: A total of 999 second trimester screening examinations were included in the study. Complete CC visualization significantly improved from 71.3% at initial protocol implementation and training to 92.1% in the current study (P < .001). A transvaginal approach was required in 4.4% of cases. The craniocaudal fetal head position had the highest success rate (98.2%) for CC visualization. The odds of nonvisualization of the CC were 2.6 times higher before 20 weeks (7.4%) than at or after 20 weeks (3.0%) (odds ratio = 2.63, 95% confidence interval [1.20-5.76], P = .012). Higher maternal BMI (≥30.0 kg/m²) was associated with increased rates of nonvisualization in obesity classes I-III.

Conclusion: Complete visualization of the CC in the mid-sagittal plane is achievable in routine second trimester morphology ultrasound examinations. Improvement in the quality of imaging is possible with a standardized protocol and training.