How is it that the blood concentration is not enough to draw blood twice with noninvasive DNA?

The main reason is that you did the non-invasive DNA too early, and the non-invasive DNA should be done at gestational age 12-26 sooner rather than later, so it is more likely that the free fetal DNA in the peripheral blood of pregnant women with gestational age less than 12 is not enough, so it is necessary to take blood tests again; In addition, it may be a small number of people who have just passed 12 gestational weeks, as well as IVF. When this happens, wait a while before drawing blood.