There is no strict rule on the latest number of weeks for non-invasive, but it is recommended that the test be done before 20 weeks. Non-invasive refers to the non-invasive DNA prenatal testing technology, which is mainly conducted through the free DNA fragments in the mother’s peripheral blood plasma, and is able to detect whether the fetus suffers from the three major chromosomal disorders, including trisomy 13-trisomy 13, trisomy 18-trisomy 18 and trisomy 21-trisomy 21, with an accuracy rate of more than 90%. Women need to be screened for Down syndrome at around 14 to 20 weeks of pregnancy, but this screening does not completely confirm whether the fetus has Down syndrome. Non-invasive DNA testing is required if the woman is at high risk, or if she is over 35 years of age, or has previously given birth to a child with trisomy. During pregnancy, women should actively cooperate with the doctor to carry out the test, and for those with special health conditions, they need to communicate with the doctor and follow the doctor’s instructions to carry out the test, so as to ensure the safety of the fetus and the pregnant woman.