Big, ‘bonny’ babies are traditionally celebrated as pictures of health, but a new international study shows women born heavy were on average nearly 4kg heavier by their mid-twenties, when they were also 50 percent more likely to develop obesity.

The study, an international collaboration between the University of Auckland-based Liggins Institute in New Zealand and Uppsala University in Sweden, provides some of the strongest evidence yet that being born much heavier than average – known as ‘large for gestational age’, or LGA – puts you at greater risk of developing obesity in adult life, regardless of length and body proportion at birth.

Researchers studied data from nearly 200,000 Swedish women who had their birth weight and length recorded in the Swedish Birth Register, and who were later assessed when they became pregnant at the average age of 26 years. Approximately one in 16 of the women were born LGA, which means at or above the 95th percentile (in the top five percent of the population) according to weight and/or length.

The heightened obesity risk was not found in women who were born longer than average but of normal weight.

Lead investigator Dr José Derraik, an honorary researcher at the University of Auckland-based Liggins Institute and at Uppsala University, says this latest evidence of a link between birthweight and future obesity risk underlines the need to support healthier lifestyle changes across families and communities.

“One in four pregnant women in Aotearoa New Zealand is affected by obesity, and babies of mothers with obesity are more likely to be heavy or LGA. So, if we can address the obesity issue, fostering in particular healthier lifestyle choices, we will also reduce the numbers of babies born LGA, in turn lessening their risks of developing obesity later in life.”

No need to panic if you were born heavy, though, says Dr Derraik. “Being at risk for something doesn’t mean you’ll get it. As with many conditions, once we’re aware of the risks we can offset them with a healthier diet, regular exercise, and adequate sleep.”

Co-researcher and Liggins Institute Professor of Paediatric Endocrinology Wayne Cutfield, who is also Director of A Better Start National Science Challenge, says: “We speculate that being too long but of normal weight is mostly genetically driven – that is, from having tall parents. However, being born too heavy is likely a result of an altered environment in utero, which includes greater nutrient flow from the mother that may cause the fetus to store more fat, so they are born heavier.”

Associate Professor Fredrik Ahlsson and Associate Professor Maria Lundgren were the Swedish co-authors from Uppsala University. The study, published in Scientific Reports, is the latest in a series from researchers at the Institute and Uppsala University in Sweden. The team has been analysing a rich body of data from national registers on Swedish women and their children to better understand the long-term health outcomes linked to events and conditions that occur before, during, and after pregnancy.

Read the article – Scientific Reports: Large-for-gestational-age phenotype and obesity risk in adulthood: a study of 195,936 women

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