The Best Time for Tang Screening Tang Screening is a prenatal screening method that detects chromosomal abnormalities and is usually performed in the early stages of pregnancy. So, when is the best time for Tang screening examination? How many weeks is the best time to do Tang Si? The following is a detailed discussion from the physical condition of pregnant women, testing accuracy, testing methods, interpretation of test results, etc., in order to clarify how pregnant women can choose the best time to undergo Tang screening examination. 1. The first thing to consider about the physical condition of pregnant women is