Although obstetricians agree that women should gain weight as part of a healthy pregnancy, two separate studies have suggested that children born to women who put on excess weight during pregnancy are likely to become overweight themselves.

Guidelines from the National Institute for Health and Clinical Excellence (NICE) suggest that, taking into account women of different builds, a total gain of almost 18kg (40lb) during pregnancy — including the weight of the foetus — is an upper limit for a healthy pregnancy. Yet two American studies involving thousands of mothers have suggested that weight gain in excess of 16kg during pregnancy will lead to babies being overweight by the age of 3, next week’s New Scientist magazine will report.

The studies were carried out by two teams, one from Harvard Medical School, Boston, led by Matthew Gillman, and a second led by Andrea Sharma, of the US Centres for Disease Control and Prevention, in Atlanta, Georgia.

The teams presented their findings last week at the 3rd International Congress on Developmental Origins of Health and Disease, in Toronto.

Guidelines issued by the US Institute of Medicine in 1990 suggest that, on average, women should experience a total weight gain of between 11.5kg and 16kg. The Harvard researchers studied a group of 770 pregnant women from Massachusetts, divided into those who gained “inadequate”, “adequate” and “excessive” amounts of weight, according to the guidelines.

Professor Gillman said: “Only the ‘inadequate’ group — a weight gain of less than 11.5 kg — gives a result that is where you want to be.”

Dr Sharma, meanwhile, scoured national health records and found a correlation between pregnancy weight gain and obesity among children aged between 2 and 4. The study of 190,000 families found that mothers who had gained more than the US institute’s recommended 16kg were more likely to have obese children.

The last two to three months of pregnancy and the first months of life are understood to be a critical period for the development of obesity, when a baby’s metabolism is learning how to adapt to what it perceives as a normal environment. The Harvard team found that the relationship between pregnancy weight gain and childhood obesity remained strong after allowing for factors such as race, smoking, income and foetal growth.

Researchers suggested that their findings could explain the marked increase in obesity in the United States, where 16 per cent of children — a threefold increase since 1980 — and 30 per cent of adults are obese.

But in Britain expectant mothers have been shown to gain even more weight than the disputed American recommendations. NICE’s latest antenatal care guidelines state: “The normal range of weight gain during pregnancy varies for each individual. Based on observational data, total weight gain ranges for healthy pregnant women giving birth to babies of between 3kg and 4kg are between 7 and 18kg.”

The World Health Organisation suggests that a weight gain of between 10kg and 12.5kg is healthy. Peter Bowen-Simpkins, at the Royal College of Obstetricians and Gynaecologists, said: “It is more preferable to think in terms of the maximum advisable weight gain as being 25 per cent of the mother’s original weight.”

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