Obese mothers-to-be need significantly more NHS care than pregnant women of a healthy weight, a study says.
The researchers spoke to staff in maternity units
NHS staff told researchers obese women need closer monitoring and special equipment, and have a higher risk of complications such as pre-eclampsia.
They also said additional abdominal fat can make it hard to feel and scan a developing baby properly.
The University of Teesside researchers, who spoke to maternity staff, called for better education about the risks.
The researchers interviewed 33 heads of midwifery, midwives, obstetricians and other professionals from 16 maternity units in the north east of England for their research in BJOG: International Journal of Obstetrics and Gynaecology.
The BJOG research is the first to look at the impact on the NHS of caring for pregnant women who are obese.
They found the women needed more tests because of an increased risk of conditions such as pregnancy-related diabetes, high blood pressure and pre-eclampsia.
Additional layers of abdominal fat make it hard to feel and scan a developing baby to check its size and heart-rate.
Obese mothers-to-be also need specialist equipment, such as modified beds and wheelchairs.
And they are also more likely to require an emergency Caesarean - and are at an increased risk of complications, such as wound infection and blood clots, after the surgery.
Professor Carolyn Summerbell, head of the University of Teesside's Centre for Food, Physical Activity and Obesity Research, said: "We're not trying to blame or stigmatise obese pregnant mothers and we would certainly not recommend that overweight mums-to-be go on crash diets.
"But our initial findings show reasons for concern with obese pregnant mothers, and there is a lack of weight management guidance and support readily available for them."
The researchers said the practice of monitoring the height and weight of pregnant women, abandoned in the late 1980s, should be re-introduced,
Professor Philip Steer, editor-in-chief of BJOG, told the BBC he had carried out a Caesarean where it had taken two doctors to hold up a woman's fat during the operation.
He said: "I don't think women realise how big a risk factor being overweight is.
"But women are between five and 15 times more likely to suffer complications in pregnancy if they have a body mass index of over 30.
"Much forward planning and co-ordination is required and public education campaigns should focus on a healthy lifestyle agenda, starting in our primary schools.
"We need to nip this in the bud."
A second, separate study, published in the journal Human Reproduction, found obese couples are three times more likely to have trouble conceiving - defined as when becoming pregnant takes more than a year - than those of normal weight.
Danish researchers studied almost 48,000 couples between 1996 and 2002.
If both partners were overweight, there was a 1.4 higher chance of a couple waiting more than a year to conceive.
It has been shown that being overweight or obese can affect semen quality in men and ovulation, conception and implantation in women.
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