To investigate the pregnant outcomes in women with very high risk of Down syndrome (DS) screening (the risk of DS ≥1/20), and to compare the differences of pregnant outcomes between pregnant women with very high risk of DS and with general high risk of DS, and explore the screening efficiency of DS prenatal screening.

From January 1, 2011 to December 30, 2015, a total of 167 singleton pregnant women with very high risk of DS screening (the risk of DS ≥1/20) in Guangzhou Women and Children′s Medical Center were selected as research subjects. According to the gestational age of pregnant women undergoing DS prenatal screening, they were divided into first trimester pregnancy with very high risk of DS group (n=75) and second trimester pregnancy with very high risk of DS group (n=92). And 6 826 cases of singleton pregnant women who received invasive prenatal diagnosis in our hospital due to high risk of prenatal screening (1/270≤ DS risk value <1/20 or 18-trisomy syndrome risk value ≥1/350) during the same period were selected as control group. The first trimester DS screening method was one-stop clinic for assessment of risk (OSCAR) which was the combination of ultrasound examination of fetal nuchal translucency (NT) and screening of maternal serum pregnancy-associated protein A (PAPP-A) and free β-human chorionic gonadotropin (f β-hCG). While the second trimester DS screening method was triple serological screening which included the screening of maternal serum alpha fetoprotein (AFP), f β-hCG and unconjugated oestriol (uE₃). Pregnancy outcomes of the three groups were followed up and compared. Chi-square test was used to compare the normal delivery rate, and incidences of fetal chromosomal abnormalities, fetal ultrasound structural abnormalities, and other adverse pregnancy outcomes among the three groups. Further comparisons were conducted by Fisher′s exact probability method with adjustment of the test level (α′=0.017). The study was in accordance with World Medical Association Declaration of Helsinki revised in 2013. Informed consent was obtained from all pregnant women before receiving DS prenatal screening or interventional prenatal diagnosis. There were no significant differences in the age and other general clinical data among the three groups (P>0.05).

①Among the first trimester pregnancy with very high risk of DS group, second trimester pregnancy with very high risk of DS group, and control group, the normal delivery rates were 48.0% (36/75), 71.7% (66/92), 96.0% (6 552/6 826), respectively, and the incidences of fetal chromosomal abnormalities were 45.9% (28/61), 22.2% (12/54), 2.4% (160/6 826), respectively, and the incidences of fetal ultrasound structural abnormalities were 12.0% (9/75), 5.4% (5/92), 0.9% (64/6 826), respectively, and the incidences of other adverse pregnancy outcomes were 2.7% (2/75), 9.8% (9/92), 0.7% (50/6 826), respectively. There were statistical differences among the three groups in the normal delivery rate, and incidences of fetal chromosomal abnormalities, fetal ultrasound structural abnormalities and other adverse pregnancy outcomes (χ²=481.120, 482.655, 98.080, 88.808; all P<0.001). Further comparisons results showed that the normal delivery rate of the first trimester pregnancy with very high risk of DS group and second trimester pregnancy with very high risk of DS group was significantly lower than that of control group, and the incidences of fetal chromosomal abnormalities, fetal ultrasound structural abnormalities, and other adverse pregnancy outcomes were significantly higher than those of control group; and the normal delivery rate of the first trimester pregnancy with very high risk of DS group was lower than that of the second trimester pregnancy with very high risk of DS group, while the incidence of fetal chromosomal abnormalities was higher than that of the second trimester pregnancy with very high risk of DS group, and all the differences were statistically significant (P<0.017). ②Among the 75 pregnant women in first trimester pregnancy with very high risk of DS group, 68 cases (90.7%) developed fetal NT thickening. Among these 68 cases of pregnant women, fetal chromosomal abnormalities were detected in 26 cases (38.2%, 26/68), fetal ultrasound structural abnormalities were detected in 9 cases (13.2%, 9/68), spontaneous abortion occurred in 2 cases (2.9%, 2/68), and 31 cases (45.6%, 31/68) had normal delivery.

The risk of adverse pregnancy outcomes in women with very high risk of DS are significantly higher than those with general high risk of DS, such as fetal chromosomal abnormalities, fetal ultrasound structural abnormalities, spontaneous abortion, dead fetus and premature delivery. As this study is just a retrospective study, whether the screening efficiency of OSCAR method in first trimester pregnancy is better than that of serological screening method in the second trimester, it still needs to be confirmed by large-sample, multi-center, prospective studies.