Research: Fat pregnancy can lead to overweight mothers

Women who gain more than 35 pounds during pregnancy could be more likely to be overweight 15 years later than those who gain less, new research suggests.

A study of 2,342 Swedish women, presented at a European obesity conference in Prague today, found that mothers who gained no more than that during pregnancy were more successful at losing their weight afterward and keeping it off.

In the Western world, the healthy amount of weight gain during pregnancy is 26 pounds for the average woman. However, the variation in weight gain among expectant mothers is huge. While some gain almost no weight at all, others put on more than 66 pounds.

The study, conducted by Dr Yvonne Linne at Huddinge University in Stockholm, Sweden, is the first to come up with a threshold at which women are likely to have trouble losing their pregnancy weight and keep it off.

“What it means is that the gynaecologist, the obstetricians, now have to have a complete new rethink of whether they should – as currently – effectively not bother about women’s weight gain during pregnancy,” said Dr Philip James, president of the International Obesity Task Force, a coalition of obesity scientists and research organisations.

“In the old days, they monitored it obsessively because they worried about poor weight gain,” said James, who was not connected with the research. “They’ve now got completely relaxed and now it’s not really of material importance to them because they always get good babies at the end.”

“If you just allow these women to rip, even if they get a handle on themselves after pregnancy, not only have you increased the risk of these women becoming obese and diabetic, but you have produced a mega baby and that baby is at risk for the rest of its life,” he said.

The study followed 563 of the women for 15 years after their pregnancy. It found that the sex of the baby did not influence whether a mother was more likely to lose her weight and keep it off.

The number of pregnancies she had over the 15 years did not matter either, though most women gain the most during their first pregnancy.

About 30% of the women gained more than 35 pounds.

Before pregnancy, 7% were overweight. A year later, 12% were and 15 years after the birth, 31% of the women in the study were too fat.

The scientists found that for a weight gain of up to 35 pounds women tended to be more successful at returning to within 4.5 pounds of their pre-pregnancy weight. Any higher and they were twice as likely to stay fat after the birth.

“It’s not 100% accurate, but it’s better than guessing,” Linne said.

One explanation for the finding is that women who gain more weight in pregnancy are less concerned about their weight anyway and so are less likely to strive to get back to their original size.

However, James said the most likely explanation is that pregnancy unmasked a hidden vulnerability to weight gain.

“You’ve now identified a susceptible woman. In fact, pregnancy was a wonderful way of testing the system to see whether they had this sensitivity to become fat,” he said. ”As they go into the menopause, they are the ones who are most likely to end up obese.”

The amount of weight an expectant mother should gain depends on her pre-existing weight and size, James said.

“If you want to simply avoid producing small babies, then the women who are thin, or short and thin, have to gain more weight – maybe 33 to 44 pounds – to avoid the handicaps,” he said.

“But as they get bigger, they need to gain less weight in pregnancy to be able to sustain a perfectly normal baby.

“Women should recognise that there’s overwhelming evidence that the quality of their diet before they become pregnant is critical.

"The new evidence is now really coming sharply in to say they should absolutely not be skinny but also they should not be overweight and they should not gain too much weight during pregnancy,” James said.