How do we calculate your due date?
There are several ways to calculate someone’s due date. We are using the Nichols’ Rule to calculate due dates because we are accounting for the first date of your last menstrual cycle, the average length of your cycles and if this pregnancy is your first child or not. The Naegele’s Rule is a commonly used formula, however, it generalizes every woman’s cycles to be 28 days long and it does not take into consideration if this pregnancy is your first child (that you’ve given birth to) or if this is your fifth. By adding these two additional important pieces of information, we can calculate a more accurate date of when you might expect your child to be born.
Can your due date change?
Absolutely. Not only will your doctor or midwife use one of these formulas to calculate your due date, he/she will also measure your baby’s growth by measuring your fundal height during each prenatal appointment and/or measure your baby via ultrasound between 8 and 12 weeks gestation. If your baby is consistently measuring bigger or smaller than expected for your gestation, your due date may change. This can happen if you have irregular cycles because it can be more difficult to determine your date of conception.
Note: Conception does not always occur on the date of intercourse. Sperm can live inside your body for up to 5 days. It all depends on when you ovulate and release an egg. If you have intercourse on the day of ovulation, you may conceive that day. However, if you have sex up to 5 days before ovulation, you will not conceive until your body releases an egg and the sperm can fertilize it. That is the day you conceive a baby.
How likely are you to go into labor on your due date?
The chances of you delivering your baby on your estimated due date are slim. This is why it’s called an estimated due date (EDD) because it is exactly that, just an estimate. Only 1 in 20 women give birth on their due date. This doesn’t account for mothers who are carrying multiples who typically deliver two are more weeks earlier. For mothers carrying singletons, you can expect to give birth within the two weeks before or after your due date. On average, first-time mothers deliver 8 days past their due date.