Your due date which is otherwise known as the day you are likely to give birth to your baby when calculated can only give an estimate of the date; most women usually give birth within 14days of their due date, that is, within 7days before the due date or within 7days after the due date.
There are three known and commonly used ways to calculate a woman’s expected date of delivery (EDD), these are: using the day of your last menstrual period (LMP), measuring the size of the uterus and using an ultrasound test.
- Using the day of your last menstrual period: the most common way to calculate your due date is to start with the first day of your LMP, add 7days and then subtract 3months. For example, if your LMP was March 10, you would add 7days to get March 17 and then subtract 3 months to get December 17. Another way to estimate your due date is to add 40 weeks to the first day of your LMP using a calendar or a pregnancy wheel.
- Measuring the size of the Uterus: the size of the uterus can be measured to give an estimated expected date of delivery but it is not accurate as many factors may interfere with the size of the uterus, thus, not giving an accurate gestational age. When the gestational age is about 12weeks, your doctor or midwife through years of training and mastery can feel the top of your uterus above your pelvis. After about 18weeks, the distance between the pubic bone and the fundus (head of the uterus in centimetres) is likely to be about the same as the number of weeks since your last menstrual period.
- Ultrasound testing: if the first two methods cannot predict the expected date of delivery, you may be asked to get an ultrasound test done, although, some doctors make it a routine to have the pregnant woman do an ultrasound test. Ultrasound tests work well to find out how long you have been pregnant, especially if they are done before 20 weeks of pregnancy.
Your due date is important because knowing the date or having an idea when you are likely to have your baby helps the pregnant woman and her spouse such that they are adequately prepared both physically and psychologically.