Pregnancy Due Date

November 12, 2012

Pregnancy Due Date

Most women start thinking about their due day the moment their pregnancy gets confirmed. It is possibly the most important day in the lives of expectant parents. They want to be ready for their baby by that date.

Due Date Calculator

Your pregnancy begins the moment your fertilized egg gets implanted into your uterus. However, it is impossible to predict this date accurately. Most experts use the first day of the last menstrual period to calculate the pregnancy due date. This date is approximately two weeks before the actual date of ovulation and conception. Your doctors as well as the online pregnancy due date calculators compute your due date by counting 40 weeks from this day.

The pregnancy due date will also help estimate the age of the developing baby, also known as the gestational age. If your doctor uses the date of ovulation or conception for the calculation, your due date will 38 weeks after the first day of pregnancy.


Although the first day of the last menstrual period as well as date of conception help calculate the pregnancy due date, you should remember that less than five percent of the babies arrive on this date. These dates, are therefore, rough estimates. The numbers can be further off the charts in women who have irregular menstrual cycles, or do not remember the first date of their last menstrual cycle.


The ultrasound is a more accurate method to determine the pregnancy due date and the gestational age of the baby. The ultrasound machines send high-frequency sound waves into your abdomen to generate pictures of your baby. You can also measure the baby, and use the measurements to calculate the gestational age. This non-invasive test can be performed as early as 5-6 weeks after the last menstrual period. The most accurate results, however, are obtained between 8-18 weeks after the last day of the first menstrual period. The results of the ultrasound and calculations from the first day of the last period together provide a relatively firm due date.

Ultrasound can establish the pregnancy due date in women with irregular periods as well. However, the results may be inaccurate if the baby is unusually large or small. It is also important to limit the exposure of pregnant women to the ultrasound radiations. The test period for the ultrasound examination should not extend beyond one hour per month.

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