Does mid-term Tang screening require fasting? Midterm screening is a prenatal examination performed by pregnant women between 16 and 20 weeks of pregnancy. It can assess whether the fetus has the risk of chromosomal abnormalities and is crucial to the health of pregnant women and fetuses. So, does mid-term Tang screening require fasting? The following explains in detail from many aspects. Aspect 1: Laboratory preparation. Mid-term Tang screening requires blood drawing for laboratory examination. In order to ensure the accuracy of the examination, the required experiments need to be prepared.