To explore the clinical application value of one-stop clinic for assessment of risk (OSCAR) for Down syndrome (DS) during frist trimester.

From March 2016 to December 2017, a total of 4 219 pregnant women who underwent OSCAR screening during frist trimester were selected into thisi study. The pre-delivery age was 17.3-51.8 years old and the gestational age was 11-13^{+ 6} weeks. All pregnant women were measured for nuchal translucency (NT) at gestational age of 11-13^{+ 6} weeks. Time-resolved immunofluorescence analysis was used to detect the serum pregnancy-related protein (PAPP-A) and free β-human chorionic gonadotropin (fβ-hCG) levels of pregnant women. The measured serum PAPP-A and fβ-hCG values were input into the prenatal screening data management software LifeCycle 4.0. The software automatically calculated the multiples of median of serum fβ-hCG and PAPP-A levels (MoM). The risks of DS and 18- trisomy syndrome were calculated in combination with the clinical data of pregnant women′s pre-delivery age, body weight on the day of blood drawing, gestational age indicated by ultrasound examination, number of fetuses, etc. For those with high risk of screening results, further amniocentesis is recommended for karyotype analysis of amniotic fluid cells. The screening result is that low-risk pregnant women will undergo prenatal screening again during second trimester. All high-risk pregnant women were followed up to 42 days after the birth of the fetus. The procedure followed in this study conforms to the ethical standards formulated by the Medical Ethics Committee of Nanning Second People′s Hospital. All pregnant women have signed an informed consent form before undergoing OSCAR screening or interventional prenatal diagnosis during the first trimester of pregnancy with the approval of the Committee (Approval No. 20190924).

① Among the 4 219 pregnant women screened by OSCAR during first trimester, the high risk rate of DS was 2.5% (103/4 219) and the high risk rate of 18-trisomy syndrome was 0.3% (11/4 219). The difference of DS and 18-trisomy syndrome in different pre-delivery age groups was statistically significant, respectively (P<0.05). Further comparison of DS high-risk rate shows that the DS high risk rate of pregnant women ≥35 years old was higher than that of other four different age ranges, and the differences were also statistically significant (P<0.05). ② NT value increased gradually with the increase of gestational age, and MoM of NT value also increased with the increase of gestational age. ③ The median serum PAPP-A level of pregnant women increased with the increase of pregnancy age, while the median serum fβ-hCG level decreased with the increase of pregnancy age. ④ Among the 4 219 pregnant women who underwent OSCAR in early pregnancy, 113 (2.7%) were at high risk and 4 106 (97.3%) were at low risk. Among 113 high-risk pregnant women, 42 (37.2%, 42/113) agreed to undergo amniocentesis or chorionic villus biopsy, and 3 were diagnosed as abnormal by karyotype analysis of amniotic fluid cells, of which 2 cases (34 and 33 years old, respectively) were DS and 1 case (22 years old) was 13-trisomy syndrome. ⑤ In 113 cases of screening high-risk pregnant women, 1 case of pregnant women had stopped growth and development before prenatal diagnosis, and then induced labor. Further follow-up screening of low-risk pregnant women found that 2 pregnant women had stillbirth and induced labor. The PAPP-A MoM values of the 2 pregnant women were abnormal during prenatal screening, which were 0.35 and 0.28, respectively (normal reference range was 0.5-2.5). ⑥ Follow-up results of 113 pregnant women screened for high-risk showed that 106 cases (93.8%) were successfully followed up and 7 cases (6.2%) were missed.

OSCAR for DS during first trimester is simple, economical and cost-effective. In addition, the abnormal PAPP-A MoM value can be used as a reference index for adverse pregnancy outcomes.