Abstract: Objective To explore the value of non-invasive prenatal test (NIPT) in pregnant women with intermediate risk after traditional Down syndrome screening. Methods From March 1 2015 to March 31 2016, a total of 2 949 pregnant women with intermediate risk after traditional Down syndrome screening who received NIPT as the second-line screening method at Shenzhen Maternity and Child Healthcare Hospital after informed consent were recruited for this study. Retrospective data analysis including the results of traditional Down syndrome screening, ultrasound, NIPT and invasive amniocentesis to fetal karyotype analysis were conducted, and pregnant outcomes were followed up. Results NIPT results were all obtained in 2 949 pregnant women with intermediate risk after traditional Down syndrome screening. Of 25 NIPTpositive cases, 24 cases received invasive amniocentesis to fetal karyotype analysis. Thirteen cases were confirmed with fetal chromosomal abnormalities including 5 cases of trisomy 21, 2 cases of trisomy 13, 4 cases of sex chromosomal abnormalities and 2 cases of other chromosomal abnormalities. In addition, 1 NIPT-positive case refused prenatal diagnosis was confirmed normal result after birth. The postnatal follow- up in NIPT- negative women did not find any newborn with chromosomal abnormality. The incidence of fetal chromosomal abnormalities in women with intermediate risk was 0.44% (13/2 949). Conclusion NIPT can be used as second-line screening method in pregnant women with intermediate risk after Down syndrome screening, which could lead to the prenatal detection of a higher proportion of fetal chromosomal abnormalities and a lower invasive-testing rate.

Key words: Down syndrome, prenatal diagnosis, fetal monitoring, fetal diseases, chromosome aberrations, intermediate risk, non-invasive prenatal test