At the age of 20, how many weeks is it usually to give birth?

Patient's question:

No

Doctor's answer:

The method for calculating the estimated due date is as follows: Add 9 or subtract 3 from the month of the last menstrual period date to determine the estimated due date month; add 7 to the day to determine the estimated due date day. If using the lunar calendar, the month calculation method is the same, but for the day, add 15.