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A due date is not an expiry date

I saw a post today on Facebook that has prompted me to write this (I see similar posts all the time, but for some reason this one inspired me!). It said something along the lines of ‘I’m 40 weeks tomorrow, my doctor wants to do a stretch and sweep. What should I do?’.

My immediate thought was, "walk away?". I have yet to find any evidence that says doctors or midwives should have their fingers in your vagina before labour has started (except if you’re being induced, but that is a different subject).

I forget who said it (feel free to message me if you know) but there is a great quote that says ‘I don’t want your fingers in my vagina unless you are giving me an orgasm’. In my opinion this is what you should say to any caregiver who wants to do an examination without good medical reason (“just to see how soon you will go into labour” is not a good reason).

But I want the subject of this article to be more about due dates. This is something that has bugged me since I did my midwifery training…

A due date is usually given so that you can know when you would expect to meet your baby – great! I’m all for making plans and having a rough ETA. And if something was to happen before that date then it is good to know if the baby is going to be premature and how much care they are going to need.

But more often than not, the due date is treated like an ‘expiry date’. And usually it is said that it is the placenta that is going to expire or stop working.

Please can someone tell me what other organ has an expiry date? Because I can’t think of one….Yes, your heart, or kidneys, or liver might stop working properly, but this is usually from disease. And in line with this, yes, if there has been ‘disease’ then the placenta might not be working well. But this will usually show up during the pregnancy. There is no other organ in the human body that has a set life span….why should the placenta be any different?

So how did we come to this ’40 weeks from the first day of the last period’ rule?

Or actually, lets go back even further in time.

How did the ancients tell time before the introduction of the Gregorian calendar?

If you said by the moon (lunar) cycles and the seasons you would be correct.

And how many lunar cycles did they say it would take for a pregnancy to be completed?


Now, how many days in a lunar cycle?

The most common answer is 28 days….because wouldn’t that be convenient - 28 days being exactly 4 weeks, and the supposed length of a woman’s menstrual cycle, plus 10 x 28 = 280 / 7 = 40 weeks, voila! The length of gestation, exactly 40 weeks…but is it?

A lunar cycle is actually 29.4 days - multiply by 10 you get 294 days. And if you divide that by 7 you get 42 week….

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However, in the 1700’s, a guy came along and said that a pregnancy should be 40 weeks from the last menstrual period (note that he didn’t specify if it should be from the first day or the last day), and that has now become ‘law’ - there is a whole long story about this came amount, but I'll tell you there was no modern scientific method involved. But this rule assumes that all females ovulate on day 14 of their cycle and that their cycle is exactly 28 days, and that babies will need to gestate for exactly 38 weeks (the first 2 weeks are not actually pregnant yet).

Another way we come to a due date is by dating scans. It is said that the earlier the scan is done the more accurate it is – this is because in early pregnancy most embryos will be the same size. The later the scan is done, the more inaccurate it is, due to the effects of genetics and ‘environment’.

However, I remember reading an article that said scans were given to sonographers to interpret and give a due date on. A few weeks later they were given more scans and asked to date those. What the participants didn’t realise was that they were actually the same scans as before and the majority of them gave different dates – meaning that interpretation of scans is also subject to human error.

If you look at documents at the hospital or centre that you are giving birth at, the space to write your ‘due date’ should say ‘estimated due date’, sometimes abbreviated to EDD. Meaning that it is an approximation, it doesn’t mean that the baby has to arrive by that date or terrible things will happen.

The World Health Organisation defines a ‘term’ pregnancy as between 37 and 42 weeks. Surely if there was compelling evidence they would be saying that ‘post-term’ started at 40 weeks?

But unfortunately, some caregivers will tell you that terrible things will happen. I have heard it said ‘nothing good happens after 39 weeks’….insert sad emoji here.

But good things do happenthe lungs and brain continue to grow and mature, the body stores up fat which can allow the baby to keep warm and regulate their blood sugar levels after they are born, and the longer we can leave a baby in utero the better (usually).

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There was recently an article published in our state newspaper by the top neonatologist that said that he was seeing a disturbing trend in ‘late preterm or early term’ births (eg 36 – 37+6 weeks) that were being done on purpose, and as a consequence believed we were producing more issues with behaviour and cognition.

So what are the risks?

I have also heard it said that for every week that pregnancy continues past 39 weeks the risk of stillbirth doubles. Now this sounds very scary doesn’t it? I can’t imagine the heart ache of going through a textbook perfect pregnancy just to have the baby die at 40 or 41 weeks….but before you stop reading this and go book in your induction for 39 weeks lets look at some numbers.

According to Evidence Based Birth (my favourite website for info on all things pregnancy and birth) the risk of stillbirth at 39 weeks is about 0.1%. Meaning that there is a 99.9% chance of not having a stillbirth (throughout pregnancy this number is actually higher - it drops to 0.1% at 39 weeks and then starts to increase again). This number does double….to 0.2% at about 41 weeks. And gets to about 0.5% by 43 weeks….meaning that at no point do you have a higher than 0.5% risk of the baby dying unexpectedly in utero before labour starts. Or conversely you have a 99.5% chance of not having a stillbirth.

Some also say that the risk of meconium aspiration increases after 40 weeks (a serious issue that can lead to severe breathing issues).

According to Rachel Reed, who writes Midwifery Thinking, there is about a 15% chance that a baby at 39 weeks will poo in utero (and therefore have ‘meconium stained liquor’ or MSL) and a 1-3% chance that they will inhale this - ie of the 15%, only 1-3% of those babies will have an issue. At 41-42 weeks the chance of them having MSL is 30% (usually because their nervous system is mature and may just release it just because, not because anything is wrong), but the risk of them inhaling it is still only 1-3%. But because there is more chance of them having MSL there is a higher proportion who will inhale it.

A baby in utero doesn’t ordinarily breath, but they can start to try if they are distressed – so my solution would be to do what you can not to distress the baby in labour!

Now, of course, some people will say any risk is too high for them. And that is fine. I am not writing this to change your mind, or to tell you to do something one way or the other. I simply want to lay out the information in an easy to read way so that you can make the decision for yourself (as all decisions should be made).

And inducing labour also comes with its risks – a 2.5 times increase in the chance of needing a caesarean for first time mothers (if you walk into a hospital in spontaneous labour you have about a 12% chance of needing a C/S, so with an induction this increases to about 30%). Fetal distress is also a risk – because the synthetic oxytocin causes contractions that are very strong and they may not be able to ‘cope’ with them. It increases in the risk of shoulder dystocia, needing an instrumental delivery, and postpartum haemorrhage (I don’t know numbers on each of those). And baby needing to be admitted to the special care nursery (or NICU) – either due to the distress they experienced during labour or because they have been born before their lungs are fully matured and therefore needing help with breathing.

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In my experience as an IBCLC, being induced can also cause issues with breastfeeding - poor feeding, and jaundice which can lead to needing to feed away from the breast and can then cause anxiety for the parents. If induction really is warranted and you want to breastfeed I would highly recommend understanding what may need to be done to protect breastfeeding while you wait for the baby to 'catch up'.

On the flip side, if there is cause for concern that your baby needs to be born before spontaneous labour starts then of course that might be the best decision, regardless of the increased risk of needing an instrumental birth or C/S, or the risk of them going to a SCN/NICU.

So when you are given your due date, please do not think of it as an expiry date. Think of it more as a guide. And evaluate your pregnancy – if there is no cause of concern for you or your baby think why ‘fix’ something that isn’t broken?

Learn more about labour and birth from a physiological and positive perspective in a HypnoBirthing class -


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