More than half of all pregnant women attending their first maternity appointment are overweight or obese, new data suggests.
Figures published for the first time show nationally that 19% of women who attended their first booking appointment in October were obese, while a further 26% were overweight.
The North of England had the highest levels of obesity, while London had the lowest.
The data, from the Health and Social Care Information Centre (HSCIC), is based on women who had their body mass index (BMI) recorded at their appointment.
Some 80 maternity providers submitted data in October, relating to more than 36,000 women attended a first antenatal appointment.
In the South of England, 18% of those attending their first appointment were obese, while a further 26% were overweight.
In the North of England, 23% were obese and a further 28% overweight, while in the Midlands and East of England, 20% were obese and 25% overweight.
London had the lowest levels of obesity, with 14% obese and a further 22% overweight.
The picture across England was similar for September, with 26% of women overweight and 21% obese.
Being obese during pregnancy increases the risk of complications such as gestational diabetes.
Women are also at higher risk of pre-eclampsia, have an increased risk of urinary tract infections and may experience problems with pain relief in labour, such as epidurals.
Obese women are also at higher risk of miscarriage and needing a Caesarean delivery.
Obesity can also cause problems for the baby such as a larger birth weight.
Research has also suggested a link between pregnancy obesity and the baby suffering heart disease and diabetes in adulthood.
Louise Silverton, director of midwifery for the Royal College of Midwives (RCM), said: "These latest figures are concerning and really do show just how much a growing problem obesity in pregnancy has become.
"Failing to tackle the causes of obesity has serious consequences for women, families and the population as a whole.
"Women should try to be an ideal weight before they become pregnant and, if not, should follow midwifery advice to manage their weight whist eating a good diet rich in micronutrients.
"After birth, women need support to develop healthy patterns of eating and exercise for themselves and their family. For women who are overweight or obese they need support and signposting to access weight-loss services to ensure that they are an ideal weight before they embark on their next pregnancy."
The data comes as Freedom of Information figures from the BBC show that NHS weight loss operations in the North East take place at double the rate of anywhere else in England.
There were 497 procedures for every million people in 2014/15, compared with 30 in the East Midlands, the figures showed.
However, the number of operations fell in the past three years.
Dr Janine Elson, spokeswoman for the Royal College of Obstetricians and Gynaecologists, said: "Obesity during pregnancy has been linked to an increased risk of miscarriage, stillbirth and neonatal death as well as pregnancy complications such as gestational diabetes, blood clots, pre-eclampsia, a more complicated labour, and severe bleeding after the birth.
"Being a healthy bodyweight increases the chances of conceiving naturally and reduces the risk of complications for both mother and baby.
"Even prior to conception women need to be thinking about maintaining a healthy weight, exercising and eating healthily to give their baby the best possible start in life.
"However, trying to lose weight by dieting during pregnancy is not recommended as it may harm the health of your baby."
Simon O'Neill, director of health intelligence and professional liaison at charity Diabetes UK, said: "It is very worrying that almost half of pregnant women attending their first antenatal appointment are overweight or obese. This means they are at greater risk of gestational diabetes, which is a very serious health condition that can cause birth defects, stillbirth and complications for the mother.
"As well as this, gestational diabetes can also greatly increase risk of Type 2 diabetes, for both the mother and child later in life, which can lead to devastating complications such as amputation, kidney disease and stroke. These complications are not only personally devastating but are also extremely costly to the NHS.
"This is why it is so important that measures are put in place to make it as easy as possible for both mums-to-be and the general public to maintain a healthy weight and lead healthier lives.
"These should include targets for manufacturers to make their products healthier, restrictions on the marketing of unhealthy food and drinks to children; and a tax on sugar-sweetened drinks.
"We want the Government to include all of these measures in its Childhood Obesity Strategy, which must be published and implemented as a matter of urgency for the sake of not just our children's but our nation's health."