Usually, four weeks of pregnancy is one trimester, so nine months of pregnancy is 36 weeks of gestation. The number of weeks of pregnancy is calculated from the first day of the last menstrual period or estimated from the ultrasound examination. For women who usually have regular periods, they should start counting from the first day of their last period, 7 days being one week, for a total of 40 weeks of pregnancy. For women with irregular periods, the week of pregnancy does not match the size of the gestational sac, so the approximate time of the last menstruation should be calculated based on the size of the gestational sac, and the week of pregnancy should be calculated accordingly to estimate the expected date of delivery. Nine months of pregnancy is 36 weeks of gestation, which is the late stage of pregnancy, when pregnant women should go to the obstetrics and gynecology department of the hospital for prenatal checkups as prescribed by the doctor. Generally, weekly prenatal checkups are required after 37 weeks of pregnancy to ensure the health of the pregnant woman and the healthy growth of the fetus. In addition, it should be noted that when a pregnant woman has symptoms such as redness, fetal descent and abdominal pain, it may be a precursor to labor, so she should be sent to the hospital in time for delivery.