To explore high risk, intermediate risk and low risk values of Down syndrome (DS) or 18 trisomy syndrome in first trimester screening in pregnant women and their fetal chromosomal abnormalities and pregnancy outcomes.

From January to December 2017, a total of 14 598 singleton pregnant women who received first trimester screening in Shenzhen Maternity & Child Healthcare Hospital Affiliated to Southern Medical University and with pregnancy outcomes were selected as research subjects. Their pregnancy outcomes were followed-up by searching information from Prenatal Diagnosis Center of our hospital or Shenzhen Maternal and Child Health Information Management System or telephoning the research subjects. Follow-up of pregnancy outcomes for live births was conducted from 1-12 months after birth or the occurrence of spontaneous abortion/stillbirth or termination of pregnancy. Among them, 6 825 cases received first trimester serological screening only, and 7 773 cases received first trimester serological screening combined with fetal ultrasound nuchal translucency (NT) detection. And 1 082 cases were with high risk of fetal DS or 18 trisomy syndrome in first trimester screening, 1 903 cases were with intermediate risk, and 11 613 cases were with low risk. There were 2 223 cases of pregnant women with advanced age (≥35-year old at parturition), accounting for 15.23% (2 223/14 598). Retrospective research method was used to collect first trimester screening results, fetal chromosomal abnormalities and pregnancy outcomes of all pregnant women. Chi-square test was used to compare screening positive rate (SPR) of fetal DS and 18 trisomy syndrome in pregnant women of different ages (<35-year old and ≥35-year old at parturition), rate of fetal chromosomal abnormalities and incidence of adverse pregnancy outcomes in pregnant women with high risk, intermediate risk and low risk of fetal DS or 18 trisomy syndrome in first trimester screening. The procedures in this study were in line with the requirements of World Medical Association Declaration of Helsinki revised in 2013.

①The SPR of fetal DS and 18 trisomy syndrome of first trimester pregnant women with advanced maternal age were 22.22% (494/2 223) and 1.30% (29/2 223), respectively, which were statistically higher than those 4.00% (495/12 375) and 0.52% (649/12 375) of pregnant women <35-year old, and both the differences were statistically significant (χ²=990.737, 18.456; P<0.001). ②There were 51 cases of fetal chromosomal abnormalities among 14 598 cases of pregnant women, 49 cases were prenatally diagnosed and 2 cases were postnatally diagnosed by neonate peripheral blood karyotype analysis, and the rate of fetal chromosomal abnormalities was 0.35% (51/14 598). Among the 51 cases of fetal chromosomal abnormalities, 26 cases were DS, and 22 case of them were high-risk of DS in first trimester screening, and 4 cases were intermediate and low risk of DS in first trimester screening, the DS detection rate was 84.62% (22/26), the rate of fetal DS was 0.18% (26/14 598); and 3 cases were 18 trisomy syndrome, all of them were high risk of 18 trisomy syndrome in first trimester screening, the detection rate of 18 trisomy syndrome was 100.00% (3/3); and 15 cases were sex chromosome abnormalities, the rate of sex chromosome abnormalities was 0.10% (15/14 598); 2 cases were 13 trisomy syndrome and 5 cases were structural chromosome abnormalities. ③Among pregnant women with high risk, intermediate risk, and low risk of fetal DS or 18 trisomy syndrome in first trimester screening, 31 cases, 7 cases and 13 cases of fetuses respectively were diagnosed as fetal chromosomal abnormalities, and rate of fetal chromosomal abnormalities of them were 2.87% (31/1 082), 0.37% (7/1 903), and 0.11% (13/11 613), respectively. Among pregnant women with intermediate risk and low risk of fetal DS or 18 trisomy syndrome in first trimester screening, 20 cases were diagnosed as fetal chromosomal abnormalities, 19 cases were prenatally diagnosed, including 17 cases with abnormal results in noninvasive prenatal test (NIPT), 1 cases of advanced age and 1 case of NT thickening; and 1 case was postnatally diagnosed. ④Excluding 51 cases of pregnant women with fetal chromosomal abnormalities, among another 14 547 cases of pregnant women with different risks of first trimester screening, the incidences of adverse pregnancy outcomes including termination of pregnancy due to fetal ultrasound abnormality, spontaneous abortion/stillbirth, premature delivery and birth defects of pregnant women with high risk, intermediate risk and low risk of first trimester screening were 9.32% (98/1 051), 5.17% (98/1 896) and 4.19% (486/11 600), respectively, and the difference was statistically significant (χ²=57.989, P<0.001).

The detection rates of fetal DS and 18 trisomy syndrome are high in first trimester screening, but not all fetal chromosomal abnormalities can be detected out. In pregnant women with intermediate risk and low risk of fetal DS or 18 trisomy syndrome in first trimester screening, fetal chromosomal abnormalities still may be found among them, and further NIPT can be helpful to detect fetal chromosomal abnormal in those pregnant women. In pregnant women with high risk of fetal DS or 18 trisomy syndrome in first trimester screening, except for high rate of fetal chromosomal abnormalities, the incidences of other adverse pregnancy outcomes, such as termination of pregnancy due to fetal ultrasound abnormality, spontaneous abortion/stillbirth, premature birth, and birth defects are also relatively high.