Let’s Talk Due Dates
Do you have a big circle around a day on your calendar that you have been nervously counting down to since you found out you were pregnant?
I’m here to tell you that you should probably plan something fun and distracting to do on that day because research tells us that only 4-5% of babies are born on that magical EDD date you have been looking forward to.
Why are we so bad at accurately predicting due dates?
Assigning a due date takes various factors into account: last menstrual period as a factor in calculating ovulation and the size of your baby at an early ultrasound. These are not exact sciences. "Naegele's Rule" which medical professionals use to calculate a due date assumes all pregnant people have a 28 cycle and ovulate on day 14 and ultrasound has a +/-15% margin of error when it comes to baby weight.
Between 2007-2011 a study in Australia used the above factors to calculate the due dates of nearly 20000 pregnant people who subsequently went on to birth babies usually within a two week window either side of the EDD they had been given. The same study suggests:
"Expectant mothers should be informed that there is only a 35% chance that they will actually go into labor during the week of their Estimated Date of Birth” Khambalia, et al. 2001"
Want to learn more 'birthy' hints and tips that are all evidence based and brilliant for you and. your birth partner ...
What else can influence your due date
Did you know that genetic factors can also play a part in when your baby chooses to arrive? Studies have shown by the most important predictor of a longer pregnancy is a family history of long pregnancies. Maybe speak to your mum, your sister and your baby's biological father's family history to find out how long pregnancies tend to be in your family.
Experts seem to conclude that on the best evidence, there is no such thing as an exact due date and even an estimated due date of 40 weeks is not accurate.
Perhaps it would be more realistic to say there is a normal range of time in which most people give birth. About 90% of pregnancies will naturally last between 37 and 42 weeks
"There is growing evidences that labour normally starts when the baby sends chemical signals to the mother’s body to say that s/he is ready to be born. It’s possible that if your labour hasn’t started, this is because your baby needs a bit longer to develop in the womb.
The concept of “being overdue” implies that all babies are “due” after the same length of pregnancy. We know that not all babies teethe, or learn to walk at the same time, so why should all babies be ready to be born after the same number of weeks in the womb? In fact, there is plenty of evidence that there is variation in this, as in anything else to do with human beings." https://www.aims.org.uk/information/item/due-date
That then begs the question about induction of labour and when it is offered, particularly if the reason is for "post dates." Induction of labour is a topic we cover as part of the Complete Birth Preparation Package so you can have all the information to make decisions that are right for you and your baby.
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