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Is your due date right?

It's not uncommon for women, before even confirming their pregnancies, to have worked out exactly when their due date might be using an online calendar tool. Those of you trying to actively conceive may even keep a close eye on this, entering the new possible outcome if you did not fall pregnant that month. I think it's fair to say that we are rather invested, if not a little obsessed, with the date we are due to expect our babies. The dating scan will often consolidate this information and leave you with one lovely, shiny date, based on being 40 weeks in to your pregnancy known as your due date. But have you ever wondered where this date comes from?

German obstetrician Franz Karl Naegele (1812) suggested counting from the expectant mother's last period, adding one year, subtracting three months, and adding seven days.

OK so let's invent a lovely pregnant lady, we'll call her Rose. Rose had her last period start on 28th September 2018 (today's date). According to the above theory as it has been interpreted, Rose is due on July 5th 2019 - congratulations Rose! The same system is used today in the UK, to add 280 days (40 weeks) to the first date of the last period.

Interestingly Naegele didn't actually specify that the last period meant the first day of the last period - it could be interpreted either that you add 7 days to the first day of the last period or add 7 days to the last day of the last period?

Over time different Doctors interpreted Naegele's rule differently, during the 1800's generally they were adding 7 days to the last day but in the 1900's most American textbooks were adopting the rule from the first day of the last period. Either way, the rule is not based on any current evidence and may not have even been intended by Naegele.

Rose was straight on to the internet when she took her pregnancy test and Googled 'due date calculator' and decided to use the NHS link. Rose has fairly irregular periods and has longer than average cycles so decided to select a 30 day cycle as her average. Rose learns that her expected due date is July 7th 2019 - congratulations Rose!

Rose is French but living in the UK, her midwife friend back home tells her how in France it is standard to add two weeks and nine months to the first day of the last period - or a total of 41 weeks, to calculate the due date. Rose's due date is now 12th July 2019 - congratulations Rose!

Rose is confused. Rose books in for her dating scan and is booked in at 11 weeks pregnant. Everything looks great and Rose is told her estimated due date (EDD) based on her baby's measurements is now 28th June 2019. Rose is even more confused!

Rose shares her happy news with her friends and family where the burning question is predominantly "when are you due?"

Rose tells everybody her due date of 28th June 2019 opting to go with the dating scan and marks the date on her calendar. She buys a cute sign to track to the days and for social media updates.

Rose read that actually only 4% of babies are born on their actual due date, but it's exciting to have to have an EDD.

You are considered at term in your pregnancy from 37 weeks until 42 weeks of pregnancy with 40 weeks being considered the average. In 2013 the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) reviewed the research and decided to change the definition of full term to 39 weeks and state that delivery should only be planned before 39 weeks when continuing the pregnancy would put the mother or baby at significant health risks. Your baby's gestational age can be off by as much as two weeks, even if you had an early ultrasound to date your pregnancy.

If you schedule a delivery before 39 weeks and your due date is off by a week or two, your baby may be born before 37 weeks gestation so it seemed wise to suggest this.

In order to make it clearer, the two organisations developed these new labels for the last weeks of pregnancy:

  • Early term:  37 weeks, 0 days to 38 weeks, 6 days

  • Full term:  39 weeks, 0 days to 40 weeks, 6 days

  • Late term:  41 weeks, 0 days to 41 weeks, 6 days

  • Post term:  42 weeks, 0 days and beyond

Let's be clear - they are all still 'term'. Your baby could arrive anywhere in this 5 week period and ultimately will choose the best time to be born with spontaneous labour. Some even suggest it should be extended to 36 - 43 weeks. In Hypnobirthing we talk a lot about the importance of words, I certainly hear a lot of new or expectant mothers using the words 'late' or 'early' when the truth is your baby is born at just the right time for you both. Gestation is individual for all women. So what's the harm in having a set EDD?

Rose's due date is here! She is still pregnant. Rose posts a social media update - 0 days until our baby is here! But it seems comfy...

The calls, texts and comments roll in. "Have you had the baby yet?" "Hurry up baby!"

All very well meaning, however Rose finds the pressure leads her to wonder.... why isn't my baby here yet?

As well as unintended pressure from her friends and family, Rose is starting to put pressure on herself which is making her feel a little anxious and stressed. She starts to think about how she can speed things along, natural forms of induction, she really doesn't want to be induced, but it was booked in at her 40 week appointment today - the next form of pressure. Rose is a bit low on oxytocin at the moment. Rose's hospital has a policy of inducing at 40 weeks + 10 days. July 8th. Rose thinks about her original calculations and how this is only a day after she thought she would be due originally, and it's before her best friend back home even suggested she would be due? But the measurement scan must be right? Right? And 40+10, that's not even 42 weeks yet?

With our induction rates continuously rising, we cannot know the average term for a women.

Evidence Based Birth suggest that:

"Based on best evidence, there is no such thing as an exact “due date,” and the estimated due date of 40 weeks is not accurate. Instead, it would be more appropriate to say that there is a normal range of time in which most people give birth. About half of all pregnant people will go into labour on their own by 40 weeks and 5 days (for first-time mothers) or 40 weeks and 3 days (for mothers who have given birth before). The other half will not.

If someone is worried about experiencing pressure from their friends to give birth by a certain time point, they may want to tell family and friends that they have a “guess date” or a “guess month,” and refrain from sharing any specific estimated due date."

So when are you due?

On KG Hypnobirthing courses we discuss your due dates at length, how accurate they may be, the implications of focusing on this date as well as the reasons it may or not be suggested to be induced. We discuss your birth rights and the evidence surrounding the policies so that you can make an informed decision about your care.

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