Knowing the exact day of conception is a difficult thing. You might even know the days that it was possible to have a pregnancy occur. However, since sperm can live in a woman’s body for up to five days, it makes it difficult to calculate exactly when conception occurred. It is not an exact science.
Another reason for this is that women can ovulate anywhere from 11 to 21 days after the first day of their last period. Ovulation varies from person to person. This is the reason why due dates are calculated from the 1st day of the last period and not from the date of conception.
At Clearway, we start doing ultrasounds when a woman is at least five weeks and one day from the first day of her last menstrual period. When we measure the tiny new life, the ultrasound machine will also give us an age based on that period as well. Therefore, when the fetus is measured at 5 weeks and 5 days, it actually could be only 3 1/2 weeks from conception.
Even though this can seem confusing, it has become a standard way of measuring pregnancy and calculating a due date. The due date is normally set at 40 weeks after the first day of the woman’s last period. For women who don’t have regular periods, this can be a problem.
Fortunately, an ultrasound can help to determine gestational age. Ultrasounds are usually most accurate between the 8th and the 18th weeks. With an ultrasound, even women who don’t have periods at all can tell how far along they are.
Since only about 5% of all babies are actually born on the due date, this is only an estimation to begin with. Each baby and each woman are unique individuals with their own timetables for birth. All we can do is give them a general idea what to expect!
Clearway: If You Think You Might be Pregnant, We’re Your Best First Step!