The fourth month of pregnancy needs to do a second obstetric examination, mainly including the following items: 1, Down’s syndrome screening: the best time is 15-20 weeks of pregnancy, through the examination of the pregnant woman’s blood concentration of alpha-fetoprotein, human chorionic gonadotropin, free estriol, and at the same time combined with the pregnant woman’s age, body weight, gestational weeks, reflecting the risk of chromosomal abnormalities in the fetus coefficient of risk; 2, ultrasound: if not checked in the past, the fourth month of pregnancy when the Ultrasound can be done once to assess fetal growth, amniotic fluid and placenta; 3, full blood tests: different regions, the examination time varies, for the basic screening of pregnant women’s blood, some of which are perfected before 4 months, not perfected at this time need to check the blood routine, coagulation function, liver and kidney function, blood glucose, as well as Hepatitis B V, A function of the five, syphilis antibodies, AIDS antibodies, etc.; 4, uterine height, abdominal circumference, Fetal heart: assess whether the uterine height and abdominal circumference are in line with the pregnancy week, under normal circumstances, the fetal heart rate in the fourth month of pregnancy is 120-160 beats per minute, check whether the fetal heart is too fast, too slow, or irregular anomalies; 5, weight, blood pressure: guide the pregnant woman to reasonably control her blood pressure and body weight, with the increase in pregnancy, the weight of the pregnant woman will change accordingly, and the growth of the body weight needs to be examined when the growth of the obvious, and at the same time, monitor the blood pressure, and be alert to the possibility of hypertension in pregnancy. Meanwhile, blood pressure should be monitored to guard against the possibility of pregnancy hypertension. The above blood tests require fasting, so pregnant women are required to fast after 12:00 p.m. the night before. In addition, amniocentesis is recommended for pregnant women >35 years of age to check fetal chromosomes.