This is also one of the biggest sticking points during pregnancy, and we often encounter mothers-to-be and their husbands in the clinic who are still unable to make up their minds after a long discussion about this. The more choices there are, the more tangles there are. The more options there are, the more confusion there is. The risk of fetal chromosomal abnormalities is calculated through professional screening software by combining information such as gestational age, maternal age and weight. There are serum only screening programs and combined programs with ultrasound soft markers. For example, the “Early Down” test involves taking the mother’s peripheral blood in early pregnancy to measure the appropriate markers and then measuring the fetal NT (nuchal translucency) to calculate the risk of chromosomal abnormalities in the fetus. Non-invasive fetal chromosome aneuploidy test (NIPT) NIPT is performed by collecting peripheral blood from pregnant women, extracting free DNA from the fetus, and using next-generation high-throughput sequencing combined with bioinformatics analysis to derive the risk of fetal chromosome aneuploidy disorders. Advantages: (1) Only the peripheral blood of the pregnant woman needs to be extracted, no puncture is required, and there is no trauma to the fetus and the pregnant woman; (2) The detection range is large: 12-24 weeks of gestation. (3) The expected detection rate is much higher than that of Down’s syndrome screening: the detection rates of trisomy 21, trisomy 18 and trisomy 13 are higher than 99%, and the false-positive rate is less than 1%, usually about 0.05%, which is an “advanced screening”. Invasive fetal chromosome testing Fetal cells are obtained by amniocentesis (amniocentesis) or chorionic villus aspiration or cord blood aspiration for cell culture and karyotype analysis, of which amniocentesis is the most commonly used. Advantages: (1) It can detect all chromosome number abnormalities and large segments of chromosome structure abnormalities; (2) It is currently the “gold standard” for prenatal diagnosis of fetal chromosomal disorders.