It is more accurate to estimate the week of pregnancy through the last menstrual period and ultrasound examination.
Women with regular menstrual cycles can calculate the week of pregnancy according to the time of the last menstrual period, from the first day of the last menstrual period to the present date is the number of days of pregnancy, according to the number of days of pregnancy and then calculate the number of weeks of pregnancy, seven days of pregnancy is one week.
Usually the menstrual cycle is more irregular, and do not remember the time of the last menstrual period, you can go to the hospital to do ultrasound projected weeks of pregnancy, according to the fetal head and buttock length, fetal head biparietal diameter, femur length and other indicators of the projected, general early pregnancy ultrasound calculation of the expected date of delivery will be more accurate.
In addition to the above methods can also be through the early pregnancy reaction time, fetal heart buds time, fetal movement time to assist in the estimation of the expected date of delivery, relatively less accurate.