Why babies born heavier may face a weighty challenge later

Girls born heavier are more likely to develop obesity by the time they're young adults, researchers have found. Photo / 123RF

Girls born heavier are more likely to develop obesity by the time they're young adults, researchers have found.

A just-published study led by Kiwi and Swedish scientists found that women born heavy weighed nearly 4kg more than an average by their mid-twenties – when they were also 50 per cent more likely to become obese.

It offered some of the strongest evidence yet that being born heavier – or what's known as "large for gestational age", or LGA - puts us at greater risk of developing obesity in adult life, regardless of our length and body proportion at birth.

The 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.

About one in 16 of the women were born LGA, which meant at or above the 95th percentile – or in the top five per cent of the population - according to weight or length.

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

Lead author Dr José Derraik, an honorary researcher at the University of Auckland-based Liggins Institute and at Uppsala University, said the new insights underlined 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," Derraik said.

"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."

Yet, for those of us born on the weightier side, there was no great need to panic.

"Being at risk for something doesn't mean you'll get it."

As with many conditions, Derraik said, once we were aware of the risks we could offset them with a healthier diet, regular exercise, and enough sleep.

So why were some babies born heavier in the first place?

"We speculate that being too long but of normal weight is mostly genetically driven – that is, from having tall parents," said co-author and Liggins paediatric endocrinologist Professor Wayne Cutfield.

"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 foetus to store more fat, so they are born heavier."

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.