Any pregnancy between 37 and 41 weeks + 6 days is called full term, <37 weeks, that is, before 36 weeks + 6 days is called preterm, and after 42 weeks is called overdue pregnancy. One prerequisite for full term is that the due date is very accurate, so check the due date before 12 weeks. To meet the criteria, it means that the menstrual cycle is very regular, for example, once every 28-30 days, and basically it is relatively accurate to predict the due date based on the last menstrual period. However, there are some people who have irregular menstrual cycles, such as menstrual cycles <24-25 days, or long menstrual cycles, more than 34-35 days, and the doctor may have to recheck the due date. Early stage can be based on the time of ovulation. Those who are doing assisted reproduction can be based on the time of embryo implantation. In case of natural pregnancy, the due date is also checked according to the early ultrasound. The exact time of full term can only be known by regular menstruation or after checking the due date.