Second‐Trimester Sonography and Trisomy 18

Objective. This report presents the findings seen on initial second‐trimester sonography in a large group of fetuses with trisomy 18. The object of this study was to describe the types and frequencies of abnormal sonographic findings seen and to further evaluate those cases in which no abnormal findings were noted. Methods. A retrospective chart review of the prenatal sonograms in cases of trisomy 18 was conducted. Results. Forty‐nine fetuses with trisomy 18 were examined by second‐trimester sonography. Multiple fetal anomalies were seen in most cases. The most frequent structural findings involved the brain (82%), heart (55%), and upper extremities (53%). Growth abnormalities occurred in 39% of these fetuses. Choroid plexus cysts were the most common individual findings. Larger cysts increased the likelihood of trisomy 18, although no fetuses with trisomy 18 had isolated choroid plexus cysts. Seven fetuses (14%) had no anomalies seen on their initial scans. In each of these scans, the fetal anatomy was incompletely visualized because of technical constraints. Six had subsequent scans approximately 2 weeks later, which showed abnormal sonographic findings. Conclusions. Most fetuses with trisomy 18 were identified by structural anomalies, typically seen in the brain, heart, and upper extremities. Larger choroid plexus cysts were associated with this aneuploidy. Technical factors, which limit fetal visualization, were noted in all cases in which no sonographic abnormalities were detected during the initial sonographic examinations. Detection of abnormal cases will rely on a completed evaluation of a routine fetal anatomic survey.