4 Things You Should Know About Your Due Date
- They are actually educated “Guess Dates”
- Only 4-5% of babies are born on her/his Due Date…
- “Post Term” refers to a pregnancy that extends to or beyond 42 weeks (not 40)
- Gestation rates for normal pregnancies can vary by up to five weeks!
- “Due Dates” are actually educated “Guess Dates”
The commonly accepted way to calculate a due date is by using “Naegele’s Rule”:
To calculate your EDD according to Naegele’s rule, you add 7 days to the first day of your last period, and then count forward 9 months (or count backwards 3 months). This is equal to counting forward 280 days from the date of your last period.
For example, if your last menstrual period was on April 4 you would add seven days (April 11) and subtract 3 months = an estimated due date of January 11.
Another way to look at it is to say that your EDD is 40 weeks after the first day of your last period.
This method assumes that a menstrual cycle was 28 days long and that ovulation occurred at day 14. Another way to calculate due dates is by using the Parikh’s Formula: Add 9 months from your first day of your last missed period, add the length of your average cycle, and then subtract 21 days. This way of calculating a due date results in a date that is about a week later than if you were to use Naegele’s Rule. A woman also might be given a dating scan to determine the gestational age based on the length of the fetus and the size of the gestational sac.
No matter what method is used to determine a due date, you should know that it is an imperfect science. An educated guess, if you will.
2. Only 4-5% of babies are born on her/his Due Date…
…And only 35% of babies are born during the week of her/his due date. That’s not a lot. In fact, you are way more likely to not have your baby on your due date than you are!
3. “Post Term” refers to a pregnancy that extends to or beyond 42 weeks (not 40)
4. Gestation rates for normal pregnancies can vary by up to five weeks!
There are many factors that seem to potentially effect the length of a pregnancy–everything from the mother’s age to the baby’s gender and beyond. This study found that “Among natural conceptions where the date of conception (ovulation) is known, the variation in pregnancy length spanned 37 days, even after excluding women with complications or preterm births.” That is a range of five weeks!
Birth is a complex and finely tuned process. Labour begins thanks to a series of unseen mechanisms, which begin to happen as the baby signals his readiness to be born, and the mother’s body responds. Science is able to do amazing things to prevent many adverse outcomes for mothers and babies today. Yet each mother and baby should be cared for based on their own personal situation, needs, and health, rather than have one rule applied to all.
At See Baby and See Baby Midwifery, we couldn’t agree more.
To read more about due dates, check out the Evidence Based Birth article on Due Dates