You're pregnant! The next question is: When is the baby due? Calculating the pregnancy due date is not complicated. There are several methods to calculate your estimated due date, but we all know that babies have their own timetables and most don't arrive on the estimated due date.

The age of the developing baby is called the "gestational age." Since the exact date of conception is seldom known, the date of the mother's last period is often used to begin calculating when the baby is due. The normal due date is 40 weeks after the first day of the last menstrual period

Another way to calculate the pregnancy due date is from conception, if known. Since ovulation and conception usually occur two weeks after the first day of the last menstrual period, the pregnancy due date is 38 weeks from conception.

Probably the most accurate way to confirm the baby's gestational age and calculate the due date is by confirming one of the above methods with an ultrasound. Ultrasound is used to measure the baby, and these measurements are used to calculate gestational age. This test is non-invasive and can be performed as early as 5-6 weeks after the last menstrual period. The most accurate results are obtained between 8-18 weeks from the beginning of the last menstrual period. The results of the ultrasound, combined with the calculated date from the first day of the last period, provide a relatively firm due date.

Women whose periods are irregular encounter difficulty using the first day of the last period or conception methods and usually must rely on the ultrasound examination. However, if the baby is unusually large or small, even the ultrasound may not provide enough information to estimate the due date.

Maria writes for Pregnancy Due Date, a site that tries to information for expectant mothers. For more great pregnancy articles, visit our Pregnancy articles archive.