What is the rate of incomplete fetal anatomic surveys during a second-trimester scan? Retrospective observational study of 4000 nonobese pregnant women

Objectives-The purpose of this study was to estimate the rate of incomplete fetal anatomic surveys during a second-trimester scan due to an unfavorable fetal position in a nonobese population. Methods-All pregnant women who came to the Altamedica Fetal-Maternal Medical Center, a specialized center for prenatal diagnosis, for a routine second-trimester scan between January 2012 and April 2013 were retrospectively included in the analysis. Patients with a body mass index higher than 30.0 kg/m2 or anterior fibroids larger than 5 cm were not included in the study. Results-Of 4000 pregnant women admitted for a second-trimester scan, 169 (4.2%) came back within 2 weeks to complete the examination because of an unfavorable fetal position. In particular, 104 (2.6%) needed visualization of only 1 view, and 65 (1.6%) needed more than 1 view. The most difficult organ to visualize was the corpus callosum, in 73 cases (1.8%); the face was not visualized in 69 cases (1.7%); the cerebellar vermis was not seen in 47 fetuses (1.1%); and the heart could not be completely examined in 40 fetuses (1.0%). Of the 4000 women, 169 (4.2%) had a nonexhaustive scan; 149 (3.7%) needed a second scan to complete the second-trimester survey; 14 (0.35%) needed a third scan; and 2 (0.05%) remained with a not completely exhaustive scan. Conclusions-There is always a small percentage of incomplete fetal anatomic surveys during a second-trimester scan, which cannot be modified by the sonographer's skill or by technical sonographic innovations.