Calculating pregnancy dates

By my calculations, you would have been eleven weeks pregnant on 12 February 12th. This means your baby would have been nine weeks old; the scan dates are exactly the same as your own calculations. Incidentally, the earlier the scan, the more accurate it is.

The confusing issue is that the number of weeks pregnant, and the baby's age, are different. On 26 February 26th your baby is eleven weeks old from conception, but you are described as 13 weeks pregnant. The number of weeks pregnant you are is the baby's age plus an extra two weeks. It sounds crazy, but there is a good reason. This is the conventional method of dating the Estimated Date of Delivery (EDD). because Many women don't know the exact time they conceived, but do know when the first day of their last period was. Therefore midwives always count the beginning of pregnancy from the first day of the last period, although most women are fertile half way through their cycle, which is two weeks later. So although the actual gestation of a baby lasts 38 weeks, the length of the pregnancy is called 40 weeks.