The calculation of the week of pregnancy depends on the regularity of the woman’s periods and cannot be generalized. If a pregnant woman had regular periods before she became pregnant, the number of days from the first day of her last menstrual period to the current pregnancy, divided by 7, will be the number of weeks of pregnancy. If you have irregular periods, you need to go to the hospital for an ultrasound examination to infer the date of pregnancy based on the size of the fetus, or you can calculate the pregnancy cycle by adding 14 days to the specific date of intercourse. Therefore, 40 weeks of pregnancy is full term, i.e. 280 days from the first day of the last menstruation to the expected date of delivery. In this case, a birth between 28 and 37 weeks of pregnancy is called preterm birth; a birth between 37 and 41 weeks of pregnancy plus 6 days is considered full term. After full term, weekly prenatal checkups are recommended to know the status of the fetal intrauterine reserve through fetal heart monitoring. If necessary, obstetric ultrasound can be performed to fully understand the size of the fetal pathways, amniotic fluid volume, placental position and function, and to be ready for delivery.