It is not possible to clearly deduce the day on which the pregnancy was conceived. Clinically, the calculation of the pregnancy week starts from the first day of the last menstrual period, and it has no effect on the calculation of the pregnancy week regardless of the day on which the fertilized egg was formed in the month of pregnancy. The calculation of pregnancy time is from the first day of the last menstruation, if the menstruation is regular, the projected time will be more accurate, if the menstruation is not regular, the time may be deviated, you need to use ultrasound to calibrate the correct time of pregnancy, but this method of projecting the time can not be clear to a certain day, there will be a certain degree of deviation. Determine the time of pregnancy, you can project the corresponding due date, generally half a month ahead of or delayed from the due date, the baby’s birth is a normal performance. In addition, during pregnancy, we should pay attention to strengthen nutrition, maintain a healthy work and rest schedule, according to the pregnancy week for regular obstetric examination, in order to observe the growth and development of the fetus.