Question

Which method is best for calculating my due date?

Answer

This whole due date thing can be so confusing! The first thing you should know is that only about 5 percent of women give birth on their so-called due date. There was recently an article in one of the obstetric journals suggesting that we shouldn't even be telling women there is a single due date — it makes more sense to talk about an "assigned week."

Anyway, here's the rule for figuring out the due date (it's called Nagele's Rule): Take the first day of the last menstrual period. Subtract three months, then add seven days. That's your due date. So if your last period was February 1, you first subtract three months (November 1), and then add 7 days. You get November 8. That should be your official due date. But here's the problem. Sperm live a few days after intercourse, and the egg lives a few days, so you might have conceived on a different day than you think. Also, now that we have ultrasound, doctors can look inside the uterus and actually measure the fetus's head and abdomen. By comparing those measurements with a normal scale, they can estimate how "old" the fetus truly is. Sometimes that doesn't match up with the due date you were given.

In the end, a pregnancy is considered a "term" (not "preterm" or "premature") pregnancy anytime after 37 weeks. What really matters is that you give birth sometime between 37 weeks and 42 weeks of pregnancy in order to have the healthiest baby. Your "due date" is really only an estimation. Hope this clears up your confusion!