How many weeks is it in the fifth month of pregnancy? Pregnancy is something every woman looks forward to. It is important for pregnant women to know how many weeks into their pregnancy they are. This article will explain in detail how to calculate the number of weeks in pregnancy and introduce how many weeks are in the fifth month of pregnancy. Pregnancy weeks calculation method Pregnancy weeks refers to the number of days from the last menstrual period to the expected date of delivery. The specific calculation method is as follows: 1. First determine the date of the last menstrual period; 2. Count 280 days forward on the calendar.