Abstract： Objective:To evaluate the effect of noninvasive prenatal testing (NIPT) as first-line screening in fetal chromosome aneuploidy screening practice, and to provide evidence for the prevention and control strategy of birth defects.Methods:Since July 2019, Hebei province had carried out the NIPT project providing first-line screening for eligible pregnant women in the area (except for those who were not applicable). Pregnant women with high risk received genetic counseling, prenatal diagnosis and intervention guidance. Low risk and false-positive ones received continuous detection and moved to prenatal diagnosis center for counseling and diagnosis if abnormities were discovered. All pregnant women were followed up to learn about pregnancy outcomes and newborn health status. Detection results and clinical data of pregnant women participating the NIPT project from July 2019 to July 2020 were collected. The detection results and effect of NIPT were analyzed.Results:(1) Basic information of the screened population: A total of 424 330 pregnant women were screened, and 423 596 were successfully detected, with a success rate of 99.83% (423 596/424 330). The age of pregnant women was (28.8±4.5) years old; the gestational age of screening was (16.6±2.3) weeks; the proportion of advanced-age pregnant women (≥35 years old) was 10.18% (43 132/423 596); in vitro fertilization-embryo transfer (IVF-ET) rate was 1.58% (6 713/423 596); the twin rate was 1.38% (5 849/423 596); the proportion of primipara was 34.23% (144 977/423 596). (2) Screening results and detection performance: totally, 325, 73 and 20 pregnant women were diagnosed with trisomy 21, 18 and 13; the sensitivity were 99.39%, 100.00% and 100.00%; the specificity were 99.98%, 99.99% and 99.98%; the positive predictive value were 75.76%, 68.87% and 21.51%, respectively. Besides, 249 190 pregnant women were received supplementary reports as well, and 255, 10 and 9 were confirmed for sex chromosome aneuploidy, other autosomal aneuploidy and deletion/duplication syndrome; the positive predictive value were 37.78%, 6.06% and 32.14%, respectively. The sensitivity of NIPT for target trisomy (trisomy 21, 18 and 13) screening in advanced-age, IVF-ET and twin pregnant women were 99.29%, 100.00% and 90.00%, respectively; the specificity were 99.93% for all; the positive predictive value were 82.25%, 61.54% and 69.23%, respectively.Conclusions:NIPT has a significant effect and good performance in the first-line screening of fetal chromosome aneuploidy in the whole population, which might provide reference for the improvement of birth defect prevention and control strategy.