At 16 weeks of pregnancy, an ultrasound is required for the Down’s syndrome screening. The main purpose of the ultrasound is to observe whether the fetus is developing normally and to measure whether the fetus’ biparietal diameter and head circumference correspond to the actual gestational weeks. In addition to the number of weeks of menopause, the application form for Down’s syndrome screening should also include the estimated gestational week of the fetus based on the fetal biparietal diameter and head circumference measured by the ultrasound. Factors affecting the results of the screening include the age, gestational age and weight of the pregnant woman, whether she has diabetes, and whether she has a history of smoking. An ultrasound is required to check the gestational week during Down screening. Down’s syndrome screening is a very important pregnancy test in the middle of pregnancy to screen for the risk of Down’s syndrome. It is recommended that pregnant women should have regular maternity checkups and prepare for the test according to medical advice.