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

Objective: 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.

Conclusions: 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.