What’s one of the first things we want to find out when we discover we’re pregnant? Or the first thing someone asks when they find out you’re expecting?
“When is your baby due?”
We pull out our calendar or open an app, enter the date of our last period, and voilà—our due date appears!
But did you know that only 5% of births happen on their due date? I’m sure you’ll agree that’s not a very accurate calculation. With odds like that, we should really question how accurate that calculation is.
What Is a Due Date and Why It Might Be Wrong
A due date marks 40 weeks from the first day of your last menstrual period (LMP). But pregnancy isn’t a one-size-fits-all process at all. We just need to look at nature to see examples of that. Not all fruit ripens at the same time – not even on the same tree! Research shows that the length of pregnancy can vary by as much as 37 days due to several factors:
Embryos that implant later tend to be carried longer
Older women often have longer pregnancies
First-time pregnancies can last longer
Family history (your mother’s pregnancy patterns)
Environmental stress near the end of pregnancy
And despite all this, being offered a stretch and sweep or induction for being “overdue” may still occur around the 40-week mark. However, guidelines like those from the World Health Organisation suggest waiting until 42 weeks+1 day, unless there’s a medical reason for earlier intervention.
The History of Due Dates
In ancient cultures and writings, we read that pregnancy lasted ’10 moons’. This would make pregnancy last approximately 295 days. Today, due dates are typically calculated using Naegele’s Rule. developed by a German obstetrician (Dr Franz Naegele) in 1812. He based his formula on only 100 women and assumed that pregnancy lasts 280 days from the first day of the last menstrual period.
But here’s the catch:
Using the wisdom of our ancient ancestors, pregnancy would last approximately 295 days (not 280 days)
Not all women have a 28-day cycle
Not all women ovulate on day 14
Conception day may differ from ovulation
- Allowances like race, age, familial history, and number of births are not taken into consideration
Looking at all these variables, it’s clear: Dr. Naegele’s rule is full of holes, and should be taken as a guideline, rather than a date set in stone.
Are Ultrasound Scans Accurate in Determining My Due Date?
Yes – to a point. First-trimester dating scans are slightly more accurate than Naegele’s Rule.
Scans in the first- trimester have a margin of error of about 5-7 days
In the second trimester, the margin widens to 8 days
In the third trimester, it stretches to around 14 days
A 2021 study comparing due dates calculated by LMP vs. a 12-week scan found:
First-time mothers:
50% gave birth by 40 weeks + 5 days
75% by 41 weeks + 2 days
Mothers who’d given birth before:
50% by 40 weeks + 3 days
75% by 41 weeks
Clearly, these findings show that we should treat a due date as a general estimate, a due window, or a due month, rather than a single day that needs medical intervention if this day comes and goes.
How your baby helps initiate labour
One of the most beautiful aspects of birth is how actively your baby participates in the process.
Towards the end of pregnancy, as your baby’s lungs and other organs reach full maturity, their adrenal glands produce increasing amounts of cortisol, the same stress hormone that helps prepare them for life outside of your womb. This fetal cortisol travels to the placenta and triggers a cascade of hormonal changes: it encourages the production of prostaglandins which help soften the cervix, getting it ready for labour.
Your baby’s lungs also release surfactant, a slippery substance that will help them breathe air after birth. A key protein in this surfactant travels into the amniotic fluid and signals to your body that everything is ready. This incredible exchange helps trigger the hormonal changes that lead to labour, showing once again how perfectly timed nature can be.
When an early birth is necessary
Every pregnancy is unique, and in some cases, birthing your baby earlier may be the best option for your and/or your baby’s health These include:
- Uterine infection
- Gestational diabetes
- Pre-eclampsia
- Placental complications
If these apply to you, your care team may suggest increased monitoring or birth via induction or caesarean section. Take your time to ask questions and do your own research before making a decision that is right for YOU.
What if I Go Past My Due Date
As you can see, due dates are not an exact science. There are accuracy issues that need to be considered when making decisions. Here’s how to stay grounded and empowered if your estimated due date arrives with no signs of labour:
Hold your due date loosely; consider telling people your due month, not the day
Plan to do something fun or relaxing on your due date
- Send a message to family and friends letting them know you will let them know when things have happened, then turn off your phone!
Trust your body and baby – they’ve brought you this far, and know what to do
Learn about your options if offered a stretch and sweep or induction. Should I have an Induction? is a blog to inform you about your choices.
Be patient – it’s excellent practice for motherhood!
Going past your due date can be emotionally tough, especially when family and friends check in constantly and there is huge pressure from the medical team to induce. Surround yourself with support, practice self-care, and try not to stress over the calendar.
I highly suggest reading ‘In Your Own Time’ by Dr Sara Wickham for an evidence and research based approach to due dates.
The Emotional Experience of Being Overdue
I’ve had many conversations with clients as they get closer to their due date, and ‘nothing’ is happening. Going past your due date can be emotionally tough, especially with contributing factors like:
- Feeling impatient because ‘nothing ‘ is happening
- Anxiety
- Added stress from friends and family
- Hospital policies and pressure
- Language being used like ‘overdue’
- Fear of induction
- Fear that something is wrong
- Feeling like you’re going to be pregnant forever
Supporting Yourself Emotionally in Late Pregnancy
Fear is such a huge factor in inhibiting labour, because adrenaline and other stress hormones are being released, which will inhibit the main hormone that is responsible for labour -oxytocin.
These suggestions will help to regulate the emotions and calm your nervous system:
- Hold your due date loosely, and tell people a due month, rather than a specific date.
- Plan on doing something fun and uplifting on your due date.
- Going back to what you have learned during your antenatal classes will steady you
- Send a message to family and friends letting them know you will let them know when things have happened, then turn off your phone!
Trust your body and baby – they’ve brought you this far, and know what to do
Learn about your options if offered a stretch and sweep or induction. Should I have an Induction? is a blog to inform you about your choices.
Be patient – it’s excellent practice for motherhood
Trust that your body won’t let you down at this last hurdle
- Deep breathing to help you feel safe
Gentle Ways to Encourage Labour
Again, I have had many conversations with anxious mums as they head closer towards their due date. There is a lot of pressure from the medical team to come in for a stretch-and-sweep, so you can ‘avoid induction’. But a stretch-and-sweep IS a form of induction. Anything that interferes with allowing your body to go into labour naturally is an intervention.
Stress and fear cause adrenaline and cortisol to be released throughout the body. Oxytocin is the hormone that drives labour, but it is a very shy hormone and won’t be released while stress hormones are present.
Here are some suggestions:
- Rest as much as possible
- Cut out the noise! Send a friendly message to your friends and family that you will be out of reach until baby is born, or there is anything to report. Then turn off your off your phone.
- Spend your time doing oxytocin-friendly activities eg. walking in nature with beloved and your dog (if you have one), eating food you love, watching a rom-com, kissing and cuddling, good sex!
- Gentle movement like walking, hip circles on the birth-ball, practicing the Miles Circuit (Here’s the link)
- Surround yourself in natural light during the day, and in the evening, use red light as blue light interferes with melatonin production which enhances oxytocin signalling (This is a great podcast to listen to)
- Take time to tune into your body and acknowledge any feelings that arise. Do any of these emotions need further attention? Perhaps reach out to someone in your trusted circle to talk to, or write it out.
- Talk to and connect with your baby. Let them know how excited you are to meet them. Writing them a letter can be very cathartic too.
When to Seek Medical Support
If at any point something doesn’t feel right, trust that intuition and contact your midwife or maternity team. You are never inconveniencing anyone by seeking reassurance or asking questions.
Being aware of your baby’s movements can help you notice changes in their usual pattern, whether that’s increased movement or reduced movement. If anything feels different from what is normal for your baby, it’s important to get in touch with your midwife.
Sudden swelling in the face, hands, or feet, particularly when accompanied by a persistent headache or visual disturbances, should always be assessed by a medical professional, as these can sometimes be signs of high blood pressure in pregnancy.
Feeling unwell, feverish, or generally not yourself may also indicate that you need additional medical support.
If your waters break before 37 weeks, have a strong or unpleasant odour, or appear brown or green in colour, you should contact your maternity care team promptly for advice and assessment.
Your Choices Still Matter
At any stage along your journey to meeting your baby, your choices need to be heard and honoured. You have the right to ask as many questions as you need to make an informed decision that is right for YOU! If you want to change your mind, you are entitled to do that too! This is your birth, and ultimately, the final choice should be yours.
I recently had a client who had discussed how important it was for her to have a general anaesthetic if she needed to have a caesarean section. Unfortunately, she did need to have surgery. We had to push for that general anaesthetic, but that is what my client wanted, and we ensured she got it, despite the recommendations for a spinal block.
Final Thoughts on Due Dates and What They Really Mean
Pregnancy is not a mathematical formula. You and your baby don’t need to conform to formulae, graphs or induction dates. Each pregnancy is a unique journey. Your baby is not a train running on a tight timetable – they’re a person arriving in their own perfect time.
If you have any questions or concerns, feel free to drop me an email or book a free 30-minute consultation. I’m here to help you feel informed, empowered, and confident in your pregnancy journey.
Wishing you patience, trust, and peace as you await your little one’s arrival.
