As the most common chromosomal aneuploidy in newborns，the patients with Down's syndrome，also referred to as trisomy 21，have clinical manifestations such as intellectual disability，growth retardation，and multiple organ malformations，requiring long-term medical intervention and social support，which brings heavy psychological pressure and economic burden to families and society. Trisomy 18 and trisomy 13 were the second and third most common chromosomal aneuploidies in live births after trisomy 21. Infants with trisomies 18 and 13 often present with extensive structural abnormalities and usually die within days to weeks after birth. There is no cure for the syndrome caused by chromosome aneuploidy at present，so it is particularly important to prevent the birth of children through effective screening and diagnosis. In recent decades，prenatal screening methods for chromosomal aneuploidies，with Down's syndrome as the main one，have been developed and updated. At present，the widely implemented screening methods include combined screening of comprehensive ultrasound and serological markers，and NIPT technology which provides cell-free fetal DNA in maternal blood，has emerged in recent years. NIPT has gradually become the first-line recommended screening strategy for Down's syndrome due to its superior screening efficiency for chromosome aneuploidies. Although serological screening is not as good as NIPT in the detection of chromosomal aneuploidies，it still has its important role in the screening for birth defects considering the screening scope，technical difficulty and cost.