The examination in the fourth month of pregnancy mainly includes routine obstetric examination and Down’s syndrome screening, through which the development of the pregnant woman and the fetus can be judged and the fetus can be screened for developmental abnormalities. 1. The fetal development can be evaluated through ultrasound testing and fetal heart monitoring to measure the growth of the fetus in the uterus; abdominal examination to determine the height of the fundus and abdominal circumference, and then observe whether the pregnant woman and the fetus are in the appropriate gestational week range; 2. Down’s syndrome screening: its main purpose is to screen the fetus for chromosomal abnormalities. The risk factor of congenital fetal defects and neural tube defects is determined by testing the concentration of alpha-fetoprotein, human chorionic gonadotropin and free estriol in the serum of the pregnant woman, combined with her age, weight and gestational week. If the test results indicate a high risk, non-invasive DNA or amniocentesis is usually recommended for further screening.