The months after pregnancy are fixed to 4 weeks and 28 days as 1 gestational month, therefore, 21 weeks of pregnancy, which is 5 months plus 1 week of pregnancy, is the middle of pregnancy. The month of pregnancy is calculated from the day of the last menstruation of the pregnant woman, 4 weeks is 1 month, 1 month 28 days. At 21 weeks of pregnancy, the fetus is basically stable, the fetal movement starts to be frequent and the range of fetal movement is relatively large, the bottom of the uterus is one finger below the belly button, and the fetal body can be touched from the abdominal wall. If the result is high risk, further amniocentesis will be required to confirm the diagnosis. The 21 weeks of pregnancy is the middle of pregnancy, which is a relatively easy stage for pregnant women, but we should not take it lightly. We need to pay attention to rest, avoid straining, do not lift heavy objects, and keep bowel movements smooth, regular rest, and strengthen nutrition.