There’s an old wives’ tale that a woman naturally puts on weight with each baby, maybe as much as one or two stones. So after a few children, women may have gained four or five stones.

Every woman puts the blame on “baby weight” but a new study says this lingering weight gain isn’t due to pregnancy. It isn’t hormonal, it’s lifestyle.

Researchers from the University of Michigan looked at data for 30,000 women who had given birth to between one and four babies.

All the women gained nearly 2lbs a year due to age but there was a striking difference between those who had given birth and those who hadn’t.

By the time their children were toddlers, mothers had put on at least one pound more each year than those who were childless.

Lead author Dr Olga Yakusheva said the difference was because “mothers tend to put the needs of their children first, so they might not be exercising or taking care of themselves”. She added: “It might also be little things like finishing food on a child’s plate.

“Many women crank up their diet and exercise for a short time to get back to pre-pregnancy weight, and often get discouraged by the results.

“But it’s much better to take a holistic approach focused on a long-term healthy lifestyle before, during and after pregnancy.”

Celebrity mothers don’t help. Having lost 3½ stone, Beyoncé appeared on the cover of People magazine four months after giving birth to daughter Blue Ivy in 2012 and said she felt “more beautiful than ever”. Gwyneth Paltrow worked out for two hours a day to get back in shape after the birth of her son Moses in 2006.

Meanwhile Victoria Beckham reportedly followed the Five Hands Diet – eating only five handfuls of food a day – to slim down for New York Fashion Week two months after the birth of daughter Harper in 2011.

Dr Yakusheva said that during her first pregnancy she gained 5 stone, and during her second she put on 4st 3lbs, despite cutting calories and weighing herself every day.

“I felt terrible,” she said. “After having a child, it’s not so much that you can’t lose the weight, but you may have less time to go to the gym, less time to food shop, and less time to prepare healthy meals.

“Sleep deprivation itself can increase food cravings and appetite, which certainly doesn’t help with weight loss. So you might just be too sleep-deprived to care to exercise or eat well.

“As long as women are healthy, that is what matters.”