Pregnant women who eat for two are putting their babies at risk, doctors say. One in 20 women are severely obese before they become pregnant and adding extra pounds before the birth compounds the problem.
Women with a body mass index of 35 or over, equivalent to a weight of 15 stone for a woman of average height (5ft 5in), have twice the risk of losing their baby in a stillbirth.
They are four times more likely to bleed after the birth, twice as likely to require seven days or more in hospital and 50 per cent more likely to need a Caesarean. They also have higher rates of fertility problems, miscarriage, blood clots, diabetes and infection.
The first national study of obesity in pregnancy was conducted by the Centre for Maternal and Child Enquiries of all 364 maternity units in the UK, of which 320 responded.
Nine out of 10 units cared for severely obese women, including 62 per cent of midwifery units, despite many lacking wide enough beds and trolleys and operating tables strong enough to take them.
Tim Draycott, consultant obstetrician at Southmead Hospital, Bristol, said: "Eating for two is a commonly held belief much reinforced by generations past. Those who start off heavier tend to put on weight very rapidly. We see women putting on a stone a month. There are significant associated complications for mothers and babies and much of that is preventable with the right care."