Role of second trimester sonography in detecting trisomy 18: a review of 70 cases

Purpose. To investigate the role of second-trimester sonographic examination in the prenatal diagnosis of trisomy 18. Methods. Out of 22,150 fetal chromosomal analyses performed between 1990 and 2004, 70 trisomy 18 fetuses were found. The sonographic findings of this aneuploidy were analyzed. Results. The average maternal age was 32.4 years; the average gestational age was 19.5 weeks. Major anomalies were seen in 61 (87.1%) of the 70 fetuses with trisomy 18; among these, cardiac anomalies were the most common (47.1%), with a 27.1% incidence of ventricular septal defects. Anomalies of the central nervous system were seen in 35.7% of cases; abnormal head shape was the most frequently detected anomaly in this group (12.9%). Fifty-six (80%) of the fetuses had at least 1 minor anomaly; of these, choroid plexus cyst was the most common (38.6%). Increased nuchal fold thickness was detected in 17.1% of cases. Conclusion. The vast majority of trisomy 18 fetuses have sonographically detectable abnormalities in the second trimester. Both the 87.1% frequency of major anomalies and the 80% frequency of minor anomalies are substantially higher than multiple biochemical marker tests could achieve. It was also demonstrated that fetal echocardiography plays a pivotal role in the diagnosis of trisomy 18. © 2006 Wiley Periodicals, Inc. J Clin Ultrasound 35:, 2007