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Patient education: Pregnancy due date calculator (Beyond the Basics)

Author
Vanessa A Barss, MD, FACOG
Section Editor
Louis Leff, MD, FACP
Deputy Editor
Kristen Eckler, MD, FACOG
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WHAT IS MY DUE DATE?

Your due date, also called the estimated date of delivery, is 280 days from the first day of your last menstrual period (LMP), if you have regular monthly periods. Most women deliver in the two weeks before or after their due date. About 4 percent of pregnant women deliver on their due date.

Due date calculator — If you have regular monthly menstrual cycles and know the first day of your last menstrual period, you can determine when your baby is due (estimated due date) and how far along you are in your pregnancy now (estimated gestational age) by using the following calculator (calculator 1).

Ultrasound — If you do not have regular monthly menstrual cycles or do not know when your last menstrual period started, you will need to have an ultrasound examination to determine your due date. This examination should be done as soon as possible because ultrasounds done after the fifth month of pregnancy are not reliable for predicting due dates. An ultrasound is commonly done to confirm the due date even in women who know their last menstrual period and who have regular periods.

WHY IS THE DUE DATE IMPORTANT?

Health care providers use the due date to figure out how far along you are in your pregnancy when you see them, both before and after your due date. A lot of decisions are based upon this information. For instance, deciding when to do certain lab tests or other tests on you or your baby and whether labor is starting too early or too late.

Literature review current through: Sep 2017. | This topic last updated: Thu Jun 01 00:00:00 GMT+00:00 2017.
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