Human pregnancy is of total 40 weeks or 280 days, or in simple terms, 9 months and 7 days. Your expected date of delivery is calculated from the first date of your last period date. Now generally everyone ovulates after 2 weeks after your periods. So you immediately don’t become pregnant immediately as your periods starts. You become pregnant 2 weeks later. But it is very difficult to determine when the ovulation takes place for everybody. Ovulation can vary even for a regular cycle. What we know for certain is when the last periods starts. So we calculate the expected date of delivery from the first day of your last periods. So it is 9 months and 1 week. Ina regular cycle, your conception would have happened 2 weeks later. This is how even the ultrasound determines the expected date of delivery. So there is uniformity between the ultrasound date and the clinical date, because we know that the first 2 weeks, you are not pregnancy, but it is still taken into account keeping the pregnancy duration as 40 weeks.
