Chromosomal abnormalities: how much can we predict by ultrasound examination in low-risk pregnancies?

We examined the rates of chromosomal anomalies detected by ultrasound investigations for the whole region of Vienna. We evaluated the data of 250 private offices, 10 clinics for Obstetrics and Gynecology, and one university Department of Prenatal Diagnosis and Therapy during the period from January, 1990, to July, 1991. The study group consisted of low-risk patients, since cases where prenatal karyotyping has been performed for other reasons than sonographic findings (for example, maternal age) were excluded from the study. An overall detection rate of 53.7% was found for the region. Structural malformations of fetuses (41.5%) were the most prominent factors leading to the diagnosis of chromosomal abnormalities. In addition, detection rate of trisomy 21 (17.6%) by prenatal ultrasonography was found to be significantly lower compared to all other chromosomal abnormalities in our study (50 to 100%).