How is the pregnancy start date determined? Pregnancy is a problem that every woman may face, but if you want to spend your pregnancy safely and perfectly, you need to determine the pregnancy start date promptly and accurately. So, how do you determine the start date of your pregnancy? This article will elaborate on the following four aspects. First, the last menstrual period time method. Most doctors will use the last menstrual period time method to estimate the start date of pregnancy because this method is simple, safe, and has a small error. The principle of this method is to calculate based on a woman\’s most recent menstrual period. It is generally assumed that the menstrual cycle is 28 days and the ovulation day is on the 14th day, that is, the start date is at the end of the period.