How is gestational age calculated

Patient's question:

No

Doctor's answer:

Count the due date starting from the first day of the last menstrual period. Since the menstrual cycle length varies among women, it is normal for the estimated due date to differ by 1-2 weeks from the actual due date. The main calculation methods are as follows: Add 9 or subtract 3 from the month of the last menstrual period date to get the due date month; add 7 to the day to get the due date day.