Some women are not particularly clear about when they are pregnant after they become pregnant. Generally, we can count according to the menstrual cycle, and for women who have a relatively regular menstrual cycle, the time of pregnancy is usually calculated starting from the first day of the last menstrual period. From the first day of the last menstrual period, to the menstrual delay in the next five days or so, after the examination and diagnosis of pregnancy, it is already about 35 days pregnant. The number of weeks of pregnancy can be determined by counting the total number of days from the first day of the last menstrual period to the present, and then dividing it by seven, which will be the number of weeks of pregnancy now. However, if your menstrual cycle is irregular or you have forgotten the time of your last menstrual period, you can estimate the duration of pregnancy based on the size of the gestational sac and the development of the embryo in the first ultrasound examination. In addition to this, the time of pregnancy can also be estimated based on the early pregnancy reaction or the time of fetal movement. For most women, early pregnancy reactions such as dizziness, nausea and vomiting, loss of appetite and flatulence will be evident around 40 days of pregnancy. Fetal movement occurs in weeks around 18-20 weeks of pregnancy, but due to individual differences in early pregnancy reactions and the timing of fetal movement, it can only be used as an auxiliary method of speculation. In general, it is very difficult to accurately know when a woman is pregnant, and there will be a certain error between the presumed time of pregnancy and the actual situation. The presumed time of pregnancy based on the last menstrual period and the ultrasound examination of the size of the gestational sac may also have a certain degree of difference, but usually will not be more than 15 days, which is a normal situation. Pregnant women do not need to worry too much about the existence of the error, which usually has little effect on the delivery of pregnant women, pay attention to regular checkups during pregnancy, ensure adequate nutrition and a happy mood.