Non-invasive DNA is usually better to be checked within 12 to 22 weeks of pregnancy. Non-invasive DNA is a testing method to determine whether there is a chromosomal disorder by drawing maternal peripheral blood and sequencing the fetal free DNA in the plasma using DNA sequencing technology, mainly used to check the three major chromosomal disorders of Down’s syndrome, trisomy 18, and trisomy 13. The optimal gestational week for non-invasive DNA testing is 12 to 22 weeks, usually around 18 weeks. If the test time is too early, the accuracy of the test results will be affected due to the low concentration of free DNA in the plasma at too small a gestational week. If the test time is too late, due to the large gestational week, once the test result is high risk, it is easy to miss the best time for further testing. During pregnancy, we should pay attention to regular pregnancy checkups and follow the doctor’s instructions to choose the appropriate gestational week for non-invasive DNA testing to ensure the accuracy of the test results.