Fasting is required for mid-screening. Prenatal screening is a series of tests performed on pregnant women who are generally at low risk by a feasible method to identify their offspring who are suspected to be at high risk of having a hereditary disease. The time for prenatal screening is not the time for diagnosis. A positive screening result implies an increased risk of disease, not a diagnosis of disease. Similarly, a negative result indicates a low risk, not complete normality. Early Down’s screening is mainly done by testing serum, pregnancy-related plasma protein A and ultrasound at 10 to 13+6 weeks of gestation. Some pregnant women miss the early Down’s screening because of their busy schedules and then, the midterm Down’s screening is done at 15 to 20 weeks of pregnancy. For Down’s syndrome screening, you should fast after 12:00 p.m. the night before the test and come to the hospital the next morning on an empty stomach. If you have any uncomfortable symptoms, you need to go to the hospital in time.