Whether or not you need to fast to have Down screening depends on whether or not it is done in conjunction with other tests. If the test is done alone, fasting is not required. If the test is done together with other tests, such as blood glucose, lipids, liver function, etc., fasting is required to ensure the accuracy of other test results. The Down’s syndrome prenatal screening test is performed by taking the blood of the pregnant woman and testing the levels of methemoglobin, chorionic gonadotropin, free estriol and other biochemical indicators to assess the presence of aneuploidy chromosomal abnormalities in the fetus, and the accuracy of these indicators does not correlate with fasting, so fasting is not necessary when doing Down’s syndrome screening alone. If liver function, kidney function, fasting blood sugar and other items need to be tested at the same time, the test will change many indicators in these items after eating, making the test results deviate greatly and the test lose its accuracy, so fasting is required. Pregnant women can consult with their regular hospitals in advance to find out if there are combined tests for Down screening and whether fasting is necessary.