Abstract: Objective To explore and analysis the values of ultrasound detection of nuchaltranslucency (NT) thickness in early pregnancy to screen for a high risk prognosis of Down's syndrome (DS). Methods The study period were from August 2019 to February 2023, and 86 cases of high-risk postpartum women who underwent registered delivery n Beiliu People's Hospital were selected as the research subjects. They were divided into the high-risk group (DS screening risk values ≥ 1/270) and the low-risk group (DS screening risk value<1/270) based on the risk value of Down syndrome.All the parturients were given Ultrasonic testing to detect the NT thickness,and the serum pregnancy associated protein-A and Human chorionic gonadotropin levels of all the cases were detected to determine the prognosis. Results There were 20 cases with a risk value of Down syndrome ≥ 1/270 that accounted for 23.26%.The age, gestational week, gestational frequency, parity, systolic blood pressure,diastolic blood pressure,and fasting blood glucose of the high-risk group were not significantly different from those of the low-risk group and were not statistically significant (P>0.05). The serum levels of human chorionic gonadotropin in the high-risk group were significantly higher than those in the low-risk group (P<0.05), while the serum levels of pregnancy associated protein-A were lower than those in the low-risk group (P<0.05). Comparing the thickness of ultrasound NT, it was found that the data in the low-risk group and high-risk group were higher (P<0.05), with the NT thickening rate of 55.00% that were significantly higher than the 9.09% of the low-risk group (P<0.05). Logistic regression analysis showed that serum pregnancy associated protein-A, human chorionic gonadotropin content, and ultrasound NT thickness were important factors leading to a high risk of Down syndrome (95%CI：0.513-0.992、2.174-6.666、1.133-7.184,P<0.001).In the high-risk group of 20 cases, there were 5 cases were diagnosed as fetal chromosomal abnormalities by amniocentesis that accounted for 25.00%, among which 4 cases were NT thickening. ROC analysis showed that the maximum area under the curve of fetal chromosome abnormalities in high-risk prognosis of Down syndrome screened by Ultrasonic testing NT thickness in early pregnancy were 0.826. Conclusion The high risk population of Down's syndrome in the first trimester of pregnancy mostly shows the increase of serum Human chorionic gonadotropin content and the decrease of serum pregnancy related protein-A content, which are also accompanied by the increase of ultrasonic NT thickness. Ultrasonic testing NT thickness in the first trimester of pregnancy can effectively predict the prognosis of high-risk population of Down's syndrome.

Key words: early pregnancy, down syndrome, transparent layer thickness, ultrasound, high risk, pregnancy related protein-A