The anticipation of welcoming a new life into the world brings joy, excitement, and a whole lot of questions. One of the most common questions expectant parents have is, “When will I give birth?” The due date serves as a pivotal milestone, giving parents a date to work towards and helping families prepare for the arrival of their little one. Today we’re exploring the concept of due dates, how they are calculated, their accuracy, and delve into some truly fascinating insights and facts about birthdays and the timing of births.
What is a due date?
A due date, also known as the estimated delivery date (EDD), is the anticipated date when a baby is expected to be born. It represents the end of the standard 40-week pregnancy period. But did you know that only around 5% of babies born in the UK come on their due date? Find out more about your pregnancy in our pregnancy guide here.
How is a due date calculated?
When you are first given a due date by a midwife or other health practitioner at the very beginning of your pregnancy, this will be calculated based on your last menstrual period (LMP). This assumes that your ovulation cycle is the standard 28 days, that you conceived on day 14, and that your pregnancy will be 280 days (or 40 weeks) long.
Later in your pregnancy, usually around the estimated 12 week mark in the UK, you will be offered an ultrasound called a dating scan. This will be able to give a slightly more accurate estimated due date based on your baby’s crown-rump length along with other checks on your baby’s development, such as a screening test for Down’s syndrome. This is considered to be the most accurate time to date a baby’s gestational age as most babies are a similar size in early pregnancy.
When your baby is measured at a later scan, it is very unlikely your estimated due date will be changed as by this time, there are noticeable differences between babies’ sizes – babies are not born as soon as they reach a specific size or weight, therefore some babies are “ready” and born at a smaller or larger size than others.
Are due dates accurate?
If there’s anything you can learn from the information above, it’s that due dates are a brilliant estimate for a round-about date that your baby will be born; in fact, it’s more likely that your baby won’t be born on their due date than they will!
There are many factors that can affect dating a pregnancy based on LMP, such as people having irregular cycles, not ovulating on day 14, the fertilised egg taking longer to implant, or simply not knowing the last date of your period.
There is still ongoing research into due dates, with two recent studies suggesting that pregnancy length should be 3 to 5 days after 40 weeks (Jukic et al. and Smith). Different cultures also consider pregnancies to be different lengths and calculate them differently – for example, in France, the estimated date of conception plus 39 weeks is your due date.
Why is a due date important?
Babies born in the 5 week period between 37 and 42 weeks are generally considered being born at “term”. But this is broken down further into the following categories: a full term pregnancy is considered as pregnancies between 39 weeks 0 days to 40 weeks 6 days; from 37 weeks is considered early term, and late term is after 41 weeks, then 42 weeks or later is post term.
The reason why these breakdowns are important is due to the small health risks associated with being born outside of full term. There is a very low risk of infants being more likely to die if they are born before 39 weeks or after 41 weeks. As a result of this, inductions are recommended at a specific pregnancy date.
One of the most common reasons that women are induced is preeclampsia which can be harmful to both the mother and baby. Prompt delivery is the only way to halt the progression of preeclampsia, but it needs to be balanced with the risks of the baby’s gestation. If the baby is delivered too early, they may suffer with long term health effects as their organs are not fully developed yet.
There are several other heightened risks of allowing a pregnancy to go too far overdue such as placenta abruption and postpartum haemorrhage. Therefore, knowing at what stage a woman is in her pregnancy can help to lower the risks to the baby, as well as to the mother.
What is the most common day of the week to be born?
There are certain dates, days of the week and times of day that you are more likely to give birth. We’ve previously shared our research into the most popular birthdays in the UK, and now we’ve researched almost 30 years’ worth of data from the ONS to pinpoint exactly what the most common weekdays to be born.
Based on birth data in England and Wales between 1995 and 2021, the most popular weekday to give birth is Thursday, and the least common is Sunday.
This research looked at the dates of birth for nearly 18 million babies born between 1st January 1995 and 31st December 2021. In this time, there were the following numbers of babies born on each day of the week on average:
- Monday: 1815
- Tuesday: 1888
- Wednesday: 1900
- Thursday: 1923
- Friday: 1906
- Saturday: 1608
- Sunday: 1521
There are, on average, more than 400 babies born on Thursdays than there are on Sundays! But why?
In the UK, births which require a scheduled intervention, such as an induction or planned caesarean, are far less likely to happen on a weekend. This instantly lowers the figures for weekends. It is likely that Thursday is the most common weekday to give birth as inductions, which can take anything from hours to days, will take place earlier in the week to avoid staffing issues on weekends.
- Sunday is always the most unpopular day of the week for births to take place.
- Despite Thursday being the most common day to give birth overall, in 2002, 2005, 2006 and 2007, Friday was the most common day to give birth, and in 2003, 2004, 2014 and 2020, Wednesday was the most common day. Unsurprisingly, these are still weekdays.
- There is a suggested correlation between a decreased percentage of births being spontaneous and an increased likelihood of Thursday being the most likely weekday to give birth. Between 2007 and 2017, the proportion of deliveries with a spontaneous onset of labour decreased from 68.6% to 52.2%.
- It is possible that the likelihood of Thursday being the most common day to give birth has stabilised in recent years due to the increase of C section births, up from 22.9% of births in 2004/5 to 30.8% in 2020/21. The length of postnatal stay for women after a C section is most commonly 1 day, therefore births are more likely to be planned for mid-week when a weekend hospital stay can more likely be avoided. This in conjunction with inductions (the rates of which have also increased similarly) happening earlier in the week, again to avoid weekend hospital stays, may help to further explain Thursdays being the most common weekday to give birth.
When will I give birth?
The exact time and day that you will give birth depends on a huge range of factors that are both personal and external. The most common way to tell whether you are likely to have a longer pregnancy is based on family history, but factors such as the below can influence the length of your pregnancy:
- Higher BMI before or during pregnancy
- Older maternal age
- A first pregnancy
- Experiencing stress in the early part of the third trimester.
Medical intervention can also influence when you give birth. Some women choose to have a planned Caesarean section which means that you will usually know the date a few weeks in advance. An induction can also bring forward the day or time that you give birth, as can an emergency caesarean or instrumental birth where the labour may have gone on longer without intervention.
Monday’s child is fair of face,
Tuesday’s child is full of grace.
Wednesday’s child is full of woe,
Thursday’s child has far to go.
Friday’s child is loving and giving,
Saturday’s child works hard for a living.
And the child born on the Sabbath day
Is bonny and blithe, good and gay.
As part of our data and research, we’ve developed a handy birthday calculator. The birthday calculator will show you which day of the week you were born on based on your birth date, and will also let you know what day of the week your next birthday is and how many days to go, so you can start planning your next party!