Babies weighing 8lb 13oz or more are considered unusually large
Women in some parts of the UK are up to five times more likely than others to give birth to super-sized babies, analysis of birth records by NationalWorld reveals.
A range of factors can influence the likelihood of having an unusually large baby, including a mother’s weight and age, genetics, gestational diabetes, and a baby being overdue.
But NationalWorld’s analysis shows widespread variation in baby weights across the country.
In some parts of England babies are up to four times more likely than others to be larger than usual, while in Scotland the worst affected areas see babies twice as likely than the national average to weigh in over the medically large baby threshold.
So where in the UK are the biggest babies born – and what proportion of babies born in your area tip the scales at a potentially problematic weight?
How big is a big baby?
Babies are considered unusually large if they weigh at least 8lb 13oz, or four kilograms – the equivalent of four bags of sugar. The medical term is foetal macrosomia.
Babies this size can lead to complications during labour, and mothers are more likely to need a caesarian section.
NationalWorld’s analysis of data from health bodies across the UK nations shows between one in seven and one in 10 babies have macrosomia, with those in Northern Ireland most likely to be on the chunkier side.
The latest data for each nation covers different time periods so the comparison between countries is imperfect. There are also differences in what the data covers, with some countries excluding stillbirths or multi-baby births.
But within each nation there is enormous regional variation in the proportion of babies born with macrosomia.
We explore the figures for each nation in more detail below – and reveal the local areas with the biggest babies.
Office for National Statistics (ONS) data shows one in 10 babies in England are unusually large.
Of 569,314 live births with weights recorded in 2020, 57,753 babies (10.1%) tipped the scales at four kilograms or more, with 596 of those weighing in at an incredible five kilograms, or 11lb.
At a regional level, women in the South West were most likely to have large babies, with 11.9% weighing at least four kilograms, followed by women in the South East, at 11.5%.
Women in London however were least likely to have large babies (7.7%). Overall, this meant big babies were more common in northern regions (10.4%) than in southern (10.1%) or midlands regions (9.8%).
The ONS does not publish data by local area.
NHS Digital however holds baby weight data for 283,600 births in England during 2021 (excluding May, for which data is missing) by council area.
Only babies born at 37 weeks gestation or later are counted in these figures, so premature babies with very low birth weights are excluded. Of the babies included in NHS Digital’s data, 10.9% were super-sized.
At a local level, it is a midlands council area that claims the crown for England’s biggest babies. In Rugby, a whopping 25.6% of babies weighed in at four kilograms, while 2.3% were five kilograms or more.
However, birth weight data was only recorded for one in every five of Rugby’s births, so the data may not show the true picture.
When looking at just areas where weight was recorded for at least half of births, West Devon moves into the top spot, with 21.6% four kilograms or heavier.
Other areas with a high prevalence of chunky babies (and where weight was recorded for at least half of births) include Derbyshire Dales (18.4%), Stroud (17.4%), Eden (17.4%), Blaby (17.2%) and Mendip (17.1%).
Mothers in Newham were the least likely to have large babies – excluding areas where the birth weight was not recorded in the majority of cases.
Just 160 out of 1,375 (5.5%) babies born in the East London borough weighed four kilograms or more. It was followed by Slough (5.8%) and Tower Hamlets (5.9%).
You can explore the figures for your area in the map below.
Around one in seven (13.3%) babies born in Scotland in the year to March 2021 had macrosomia, according to Public Health Scotland (PHS) figures.
But women living in the islands of Orkney and Shetland were almost twice as likely to have big babies – 24.4% and 26.2% respectively.
Babies from Dumfries and Galloway were the next heaviest, with 16.2% at least four kilograms, followed by Tayside (14.9%) and Western Isles (14.8%).
Shetland’s figure was the highest for any local area in the UK.
Scotland’s figures only count live singleton births (those involving just one baby) however, with twins, triplets and other babies born in multiple cohorts excluded.
Non-singleton babies are generally smaller than singletons, according to the Royal College of Obstetricians and Gynaecologists, so this could affect the comparison with other countries, where multi-baby births are included.
NationalWorld contacted Shetland and Orkney health boards for comment on the high prevalence of large babies in their islands.
A spokesperson for NHS Orkney said: “This isn’t something which has been investigated at present.”
Figures for each health board area in Scotland are available in the map below.
Babies in Northern Ireland are the most likely in the UK to be super-sized, with 13.8% of those born in 2018-19 weighing at least four kilograms, according to Health and Social Care (HSC) Northern Ireland data.
There was significant variation across the country. The biggest babies came from Newry, Mourne and Down (15.4% at four kilograms or more) followed by Fermanagh and Omagh (15.3%) and Mid Ulster (14.9%).
Women in Belfast were the least likely to have large babies, with 11.9% of babies affected.
Unlike other nations, Northern Ireland’s local figures include stillbirths, where birth weights are more likely to be low, which could bring down the proportion of large births when compared to other local areas in the UK.
You can explore the data for each local government district in the map below.
Figures published by the Welsh Government for 2020 show 11.9% of live births involved a baby weighing at least four kilograms.
Powys Health Board, in the centre of the country, was the area with the highest prevalence of large babies, at 14.2%.
In the capital city Cardiff in comparison only 10.7% of babies had macrosomia.
Figures are based on the health board providing maternity services, rather than where the mother usually lives.
Explore the figures by health board in Wales in the map below.
What causes macrosomia - and are there any risks?
Some mothers are more likely to have larger than average babies, including those who have diabetes or develop diabetes during pregnancy, or have a high Body Mass Index (BMI).
Professor Asma Khalil, spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “While there is an increased risk of complications if a baby is [four kilograms], the majority of women do not have any complications and their baby is born safely without any problems.”
One increased risk concerns shoulder dystocia, she said, where a baby’s shoulder gets stuck behind the pelvic bone during delivery. A mother will usually need extra help to free the baby.
She continued: “There is also an increased risk of the mother having heavier bleeding than normal after birth, and vaginal tears if having a vaginal birth.
“In some cases, if a woman had diabetes, they may be offered an early induction of labour, or a planned caesarean birth.”
Are babies getting bigger?
In recent decades the average baby born in England and Wales has become heavier, according to a 2018 study published in the British Medical Journal.
Some anti-obesity campaigners have warned that unusually big babies are becoming increasingly common due to a rise in obesity among pregnant women.
Despite this, the data for each nation shows there has been no increased likelihood of newborns weighing four kilograms or more during the last decade across each UK nation.
In England, the proportion of super-sized babies has fallen from 11.4% in 2010 to 10.1% in 2020, the ONS data shows.
In Wales, prevalence is down slightly from 12.1% to 11.9% over the same period, reaching a peak of 12.2% in 2014.
The proportion of babies weighing four kilograms in Scotland fell from 14.1% in the year ending March 2011 to 13.3% in the year ending March 2021 – although there was an increase in the last year.
And in Northern Ireland, prevalence is down from 15.1% in 2010-11 to 13.8% to 2018-19.