CNV, or Gene Copy Number Variation, is a test to check whether the fetus has abnormal chromosome strips and whether there are deletions, duplicate segments, etc. of genes. CNV requires the extraction of fetal cells need to be examined by amniocentesis to extract fetal cells from the amniotic fluid, and then the fetal cells are studied for genetic CNV. Some pregnant women also choose to undergo non-invasive DNA testing, where fetal cells are extracted from the pregnant woman’s blood for CNV testing, but this will have a relatively high rate of false positives and missed diagnoses. Pregnant women whose Down’s test results are high-risk, as well as high-risk pregnant women whose expected age of delivery is greater than or equal to 35 years old, etc., are recommended to undergo amniocentesis CNV test to avoid the birth of babies with serious genetic abnormalities.