More than one expecting mom has circled her pregnancy due date on her calendar and then been disappointed when the day passed uneventfully. There are a number of methods used in pinpointing an accurate due date, but none are fool-proof.

The best way to look at a pregnancy due date is as a pregnancy window with quite a bit of wiggle room. With good prenatal care and a healthy mom and baby, a typical pregnancy can vary from 38 to 42 weeks gestation. That means you could be wrong by a month!

First babies tend to have longer gestational periods and women of color often have shorter pregnancies. Sometimes a pregnancy due date is inaccurate because the dating of the pregnancy wasn’t done correctly. Dating done by ultrasound is more accurate than dating by last menstrual period. Keep in mind that babies often come on their own schedules, regardless of when mom has scheduled their pregnancy due date.