It is your first appointment with your doctor and you are eager to ask him the question “When my baby will be born?” Calculating your due date will give you an estimate about your baby’s birth date. Using online electronic calculators, doctor’s wheel calculators or Naegle’s rule would only give you a date that is typically inaccurate.
Pregnancy lasts 42 weeks as a maximum. 80% of women deliver between the 38th and the 40th week. All calculators use last menstrual period (LMP) method to calculate due dates. Since we cannot specify the exact day for ovulation, we use the LMP date and we estimate that ovulation occurs on the 14th day after LMP then we add 266 days to it in order to have the due date.
Here is a simple way to calculate your due date at home:
(LMP + 7 days) – 3 months = Due Date Example: (October 1st 2011+ 7days) – 3 months = August 8th 2012
Other methods are also used to determine due dates as ultrasound which measures the baby’s length and gives the gestational age. We can also measure the uterine size to evaluate the pregnancy term. In some cases these 2 methods can be inaccurate if the baby is small or large or the height of the uterus does not match the gestational age.