This kit is designed for the in vitro qualitative detection of cell-free DNA (cfDNA) in the peripheral blood plasma of high-risk, singleton pregnant women at 12-24 weeks of gestation. It constructs a DNA library using cell-free fetal DNA from the peripheral blood plasma of singleton pregnant women. It constructs a DNA library using cell-free fetal DNA from the peripheral blood plasma of singleton pregnant women. Analysis of chromosomal numerical abnormalities in chromosomes 21, 18, and 13 of fetal cell-free DNA (cffDNA) in samples via high-throughput sequencing technology, followed by assessing the risk of trisomy 13, trisomy 18, or trisomy 21.