Purpose. The evaluation of the effectiveness of ultrasound markers in the diagnosis of fetal chromosomal abnormalities, based on the results of combined prenatal screening in the Republic of Tatarstan in 2012-2019.

Materials and methods. The study includes a retrospective analysis of pregnant women who underwent the combined prenatal screening at 11-14 weeks of pregnancy for the period of 2012-2019 in the Republic of Tatarstan. According to the result of screening, pregnant women were divided in groups of high (>1:100), medium (1:100-1:1000) and low (<1:1000) risk. In the second and third trimesters, when ultrasound markers of abnormalities were detected, a genetic consultation was carried out in order to determine the need for an invasive diagnostic method. Results. During this period, 283835 pregnant women were examined, and 1143 fetuses with chromosomal abnormalities were revealed. Down’s syndrome was detected in 624 fetuses (54,6%).  From the medium and low risk group, 69 fetuses with chromosomal abnormalities were detected in the second and third trimesters and after birth. Of these, 33 cases were diagnosed prenatally, and 36 cases were diagnosed in postnatal period.

Discussion. Our results showed that strict keeping of algorithm of ultrasound diagnostics, quality control of the work of ultrasound specialist of prenatal centers and regular analysis of false-negative cases can increase the sensitivity and effectiveness of the diagnosis of chromosomal anomalies in the fetus.

Conclusion. The sensitivity of combined prenatal screening during the study period was 88%, with the proportion of false-negative cases of 12% in the medium and low risk group. In these groups, additional ultrasound examinations in the II and III trimesters of pregnancy revealed 47.8% (33 cases) of Down syndrome in fetuses. The structure of malformations in these groups is marked by rare combination of several ultrasound markers in one fetus, often isolated, "soft" ultrasound markers.