Why Your Baby's Due Date is Completely Wrong!

If you are pregnant or ever have been, you will know that very often the first thing people ask you is when is baby due? So ingrained in our culture is the idea of a due date, it may often be one of the first things we do ourselves. Yet we don’t recognise that the very idea of a due date is artificial and that setting one is in fact a medical intervention in itself.

We are so used to diarising and planning our lives that it seems natural to do the same for a baby. After all, don’t we want to be prepared and have everything in order at the ‘right’ time? We may need to plan our work, our childcare, manage existing children if there are any, plan a holiday, order baby equipment, book in pregnancy appointments - there is quite a large ‘to do’ list.

More crucially though, the concept of a due date has a huge impact on your medical care in pregnancy and is a deciding factor in determining medical interventions to end pregnancy. Once a due date is in place, the concept of the baby being overdue or late is also created. Deadlines are put in place which state if the baby is not here by ‘x’ date then we will start the induction process.

And the reasons for induction are being expanded with NICE recommendations having been updated  in 2021 to start the process even earlier, offering membrane sweeps from 39 weeks. It is quite alarming that in the 10 years from 2012 to 2023 the rates of induction rose from 23% to 33% according to NHS England figures.

This date has big implications to the healthcare advice and treatment given to a pregnant woman.

But what if a due date is little more than a human construct that does not reflect the reality of pregnancy? How many women are having untimely and unnecessary interventions? Surely, you would think something given the weight of a due date, that can be the deciding factor in starting medical procedures would be fully researched and backed up by evidence. Apparently not.

Let’s rewind a little a look a the origins of a due date.

In the early 18th century Franz Naegele a Dutch doctor made famous an algorithm to estimate a date of birth, which he determined was 9 months and 7 days after the woman’s last menstrual period. It generally works out at 280 days, or 10 lunar months. This is known as Naegele’s rule and is still being used today to fix due dates in pregnancy. So what’s wrong with that?

First, it was not made clear in the original writings whether this was from the beginning or end of the bleed which could in fact add another 5-7 days. However, textbooks decided to interpret this as the first day of the bleed.

Second, this is assuming all women have the same menstrual cycle and fertile window in which to conceive. Note the date is counted from the period not from date of conception. The conception date is assumed from the menstrual cycle itself and is in reality most likely not accurate.

Third, there is no original evidence of research being done to prove this timescale. It seems to be based largely on historic cultural norms rather than any actual study of the length of real pregnancies. Aristotle seems to be the first written reference of 10 lunar months as the duration of pregnancy.

Fourth, the creation of this algorithm was not originally done for medical reasons but in fact to determine paternity for legal reasons. In the 1700’s they could not have known the potential impact it would have on triggering medical interventions.

Fifth, modern research shows that a range in lengths of pregnancy is normal and that Naegele’s rule doesn’t accurately calculate even the average length of pregnancy. Both a 2001 and 2013 study showed the average length was 40 weeks plus 5 days. Other research from 1967 evidenced that 70% of babies were born in a 3 week window from 10 days prior to 10 days after the ‘due date’. Which also means around one third were even earlier or later than that.

My experience in 20 years of practise certainly is in line with this research. I have always had a gut feeling that due dates were somewhat arbitrary and have seen varying lengths of pregnancy ending in spontaneous labour. It seems to fall within the range of normal that babies can arrive a couple of weeks either side of a ‘due date’. So, in effect there is a due month rather than a due day.

There is no standard length of pregnancy, like with all humans there is variety, and that variation is normal, natural and healthy, just as perfectly healthy babies can be different sizes and weights, develop in different ways at different times. And just as our menstrual cycles are different lengths and degrees of heaviness with different symptoms. Using a one size fits all is great in terms of managing (think factory uniformity) but does a disservice to many women.

Often our instincts and inner knowledge are dismissed or overruled. Even when an exact conception date is known, a due date may be adjusted following a scan based on the size of the baby, as though all babies all over the world are exactly the same size at a certain number of weeks regardless of the size of their parents. And it is the setting of a due date that is the first medical intervention in a pregnancy from which further interventions ae justified.

If you have already had a baby, how much stress did you feel at the end of pregnancy based on your due date? Did you feel pressure from medical staff to ‘get things moving’ along with talk of increasing risks? Did you have family and friends phoning daily to ask is baby here yet?! Perhaps you are in that position right now, feeling pressure to be induced.

All of that pressure and stress is the exact opposite of what mums need as they approach labour. Stress in fact inhibits labour and can raise blood pressure so it becomes a self-fulfilling prophecy that justifies the intervention. We need to be relaxed calm and confident for our body to do what millennia of evolution has designed our bodies to do. Babies also need to come when they are ready without additional stress, some take longer than others.

So how would you feel if you were given a month in which to expect your baby? To be told that a 4 week window of delivery is perfectly normal and healthy. That you would just have watchful waiting during this time with no pressure about being ‘late’ or ‘at risk’.

Of course all pregnancies are unique and sometimes there are genuine medical conditions or health concerns for the mother or baby where interventions are necessary. However, these decisions need to be made on a case by case basis, specific to each pregnancy, not on the basis of an algorithm.  

In my practise I love to support and empower pregnant mothers to make truly informed choices about what care they receive. I also love seeing the effect reflexology has in easing pregnancy symptoms, offering deep relaxation and supporting spontaneous labour. When we work with the body, supporting its natural functions, we not only reduce stress but promote a healthy comfortable pregnancy.

If you would like to work with me, you can find out more about my pregnancy reflexology packages  or simply get in touch to discuss your needs.