Prenatal diagnosis of trisomy 13: analysis of 28 cases.

OBJECTIVE

The purpose of this study was to investigate the role of second-trimester sonographic examination in the prenatal diagnosis of trisomy 13.

METHODS

Of 22,150 fetal chromosome analyses, 28 fetuses with trisomy 13 were found between 1990 and 2004. Sonographic findings of this aneuploidy were analyzed in this study.

RESULTS

The average maternal age was 32.4 years; the average gestational age was 19.5 weeks. There was an 89.3% (n = 25) total prevalence of sonographic abnormalities in fetuses with trisomy 13 in this series. Major (structural) malformations were seen in 23 cases (82.1%), whereas minor anomalies were detected on sonography in 16 cases (57.1%). Although in 2 fetuses 1 minor anomaly was the only sonographic sign of trisomy 13, other cases with minor anomalies (87.5% [n = 14]) were multiplex malformations, in which combinations of major and minor anomalies were detected on sonography. The most frequently seen structural abnormalities were central nervous system and facial anomalies (64.3% [n = 18]). Among central nervous system anomalies, ventriculomegaly and holoprosencephaly were seen most frequently. Cardiovascular anomalies were detected in 53.6% (n = 15) of the fetuses with trisomy 13. This high frequency underlines the importance of echocardiography in diagnosing this aneuploidy. Among minor anomalies, increased nuchal translucency (21.4%) and echogenic bowel (17.9%) were the most common findings.

CONCLUSIONS

Second-trimester sonographic examination is capable of showing anomalies that are characteristic of trisomy 13; thus, the scan can indicate whether fetal karyotyping is advisable. Incorporation of careful assessment of the fetal cardiovascular system by sonography certainly increases the detection rate of trisomy 13.