Women can usually estimate the time of conception by the time of the last menstrual period and the method of ultrasound. 1. Time of last menstruation. Generally, the time of pregnancy is counted from the first day of the last menstrual period. For women with regular menstrual cycles, ovulation is the easiest time to conceive, and ovulation usually occurs about 14 days before the onset of menstruation, so the number of days of pregnancy can be estimated according to the time of the last menstrual period, and then subtracted from 14 days is the approximate time of conception. 2. Ultrasound examination. If your menstrual cycle is not regular, and it is not easy to calculate the time of ovulation through the last menstrual period, you can go to the hospital to do ultrasound examination, according to the size of the gestational sac, the development of the fetal buds and the fetal heart, as well as the week of pregnancy, you can estimate the approximate time of conception. However, the projected time of conception is only an estimated value, and can not accurately project the specific time, and the clinic does not use the date of conception to project the gestational week, it is the time of the last menstrual period to calculate the number of days of pregnancy, the last menstrual period and ultrasound projected gestational week of the pregnancy week of the difference of about 1 week is normal, pay attention to the good pregnancy checkups, supplemental folic acid can be.