Does anyone actually give birth on their due date?

22464 Dr Fysh - Aug 14, 2018

The question everyone will ask you, constantly, throughout your pregnancy is: “When are you due?” We seem to be obsessed with due dates but the reality is only 5% of babies actually arrive on the assigned day.

Your due date is calculated by taking the first day of your last period and adding 280 days, i.e. 40 weeks. So if your last period started on 1st January your due date would be 7th October (assuming it wasn’t a leap year).

But this method assumes that your periods are exactly the same each month, beginning exactly 28 days apart. In reality that isn’t how it always works so if your cycles are longer than 28 days you’re likely to deliver later than your due date. If your cycles are shorter, expect baby to arrive a little earlier.

A much more reliable way of ascertaining what stage the pregnancy is at, is the first trimester scan. The length of the foetus and size of the gestational sac are used to assess the age of pregnancy so far and your due date may be adjusted if the two figures don’t match up. 

But even with both these ways of calculating the date, the system is still extremely unreliable. The truth is that we don’t fully understand what triggers a woman going into labour so we rely to some extent on guesswork.

In fact your best indicator might be your own previous pregnancies or even your mother’s experience.

If your mum delivered late, there is a good chance you will too.

The vast majority of women – around 80% - deliver between 37 and 42 weeks.  About 11% deliver prematurely.  The remaining pregnancies go beyond 42 weeks or ‘post-term’.

US newspaper The Boston Globe carried out a study which found that the most common arrival date was 7 days before the official due date.

It found that first children tended to stay put for a little longer. On average, they showed up two or three days early. Second and third children arrive five to six days early.

The older you are, the more likely you are to give birth early.

The important thing to remember is that the due date is only ever intended as a guide and once you’re baby arrives you won’t care at all!

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About Dr Fysh

Dr Fysh

Dr Fysh is one of the country’s leading consultant paediatricians, currently a consultant at The Portland Hospital for Women and Children, and a Fellow of the Royal College of Paediatrics & Child Health and the Royal College of Physicians. Having experienced first-hand the suffering caused by serious medical conditions to babies and young children and the emotional and financial strain that this can place on parents on a daily basis. He joined the board of directors as Chief Medical Officer and has been instrumental in the building of the NurtureFirst product. 

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