Seven clinics reported births of so-called "sumo babies" in 2013 - including two where the babies weighed more than 6kg.
Tam Fry, of the National Obesity Forum, said that although some mothers suffer from medical conditions, which increase the size of the baby, most just overeat.
He said: "Quite simply, the number of pregnant women who are obese at the start is increasing."
It is thought that 82 per cent of children who are obese will continue to be overweight.
As they have the same kind of nutrition as their parents there is a continuous upwards spiral.
"Successive governments have not really addressed the obesity problem. It starts at conception and sometimes even before then."
Mr Fry also suggested that the number of women having caesareans was increasing due to the increasing size of their babies.
"Some babies are so fat they cannot come out naturally. Women have to understand that they have to keep themselves in shape due to the huge responsibility they have of producing the next generation. If we get it wrong, it's a vicious circle and it will just go on and on and on."
Toddlers are also being hospitalised for being obese, with 28 two-year-olds and 33 three-year-olds admitted since 2011, Laura Connor revealed in her Sunday Mirror investigation.
The average weight of a baby boy in the UK is 7lb 8oz (3.4kg) and for a girl it is 7lb 4oz (3.2kg).
Childhood obesity can lead to a number of medical problems including diabetes, heart disease, strokes and cancer.
A Royal College of Midwives spokesman said: "It starts pre-conceptually. If a woman is trying to get pregnant then she should already be eating healthily and not drinking or smoking.
"It is a common myth that the woman should eat for two. Really, she should be just taking in lots of vegetables and a balanced diet.
"Long walks and gentle jogs can also help."
- Daily Mail
