The National Obesity Forum said that the number of larger-than-average newborns has been increasing since the 1960s because of the rising number of overweight and obese pregnant women.
The comments were made after figures revealed almost a third of maternity wards have delivered babies weighing more than 12lb.
The average weight of a newborn is 7lb 4oz for a girl and 7lb 8oz for a boy. Yet reports found that 38 out of 139 English maternity units had delivered children weighing in excess of 12lb in the last year. Tam Fry of the National Obesity Forum said: "We expect this to continue rising until something is properly done."