How is the Conception Time Calculated?

The exact time of conception is generally difficult to determine, but medically, the expected delivery date is calculated from the first day of the last menstrual period. The pregnancy period is 280 days in total. Due to the different physiological cycles of each pregnant woman, there may be some errors in the estimated delivery date, generally ranging from one to two weeks, which will not have a significant impact on the calculation of pregnancy time.

1. Calculation Based on the Last Menstrual Period

Many hospitals calculate the time based on the last menstrual period. For example, Ms. Zhang's last menstrual period was March 13, 2008, and her estimated delivery date is around December 20, 2008. Ms. Li's last menstrual period was May 28, 2008, and her estimated delivery date is around March 5, 2009. You can also count back from the first day of the last menstrual period to the 280th day to get the expected delivery date.

2. Calculation Based on the Date of Fetal Movement

Some women cannot clearly remember the date of their last menstrual period and can calculate it based on the date of fetal movement. Generally, fetal movement begins at 18-20 weeks after pregnancy. The calculation method is: for primiparas, add 20 weeks to the date of fetal movement; for multiparas, add 22 weeks to the date of fetal movement.

3. Calculation Based on the Basal Body Temperature Curve

Body temperature can also be used as a basis for judgment. Take the last day of the low-temperature segment of the basal body temperature curve as the ovulation day, and calculate back 264-268 days from the ovulation day, or add 38 weeks.