How many days does it take from pregnancy to birth?

The calculation method is to subtract 3 months or add 9 months to the first day of the last menstrual period, plus 7 days. For example, the first day of the last menstrual period is April 21, 2000, and the expected date of delivery is January 28, 2001. If only the first day of the last menstrual period of the lunar calendar is remembered, it should be converted to the Gregorian calendar and the expected date of delivery calculated. It must be pointed out that the actual date may differ from the expected due date by 1 - 2 weeks. If you don't remember the date of your second period, you can ask your doctor to estimate it based on the time when early pregnancy starts, the time when fetal movement starts, and the length of the uterus as measured by a ruler. This method is widely used by obstetricians and gynecologists at this stage. However, because many pregnant women don't know the menstrual cycle or the irregular ovulation date, the results can be affected. Conversely, if the menstrual cycle is accurate, the accuracy of the algorithm can reach 100%.