Auckland study reveals over-term babies have higher risk of obesity
Obese women may want to check if they over-stayed in the womb.
Baby girls born late, at 43 weeks or more, are more likely to grow up obese, according to a new study by Auckland University's Liggins Institute.
The international study found these overdue female babies were 12 per cent more likely to grow up obese.
Baby boys have not yet been studied.
Liggins Institute lead author Dr Jose Derraik said the findings empowered women who were born post-term to make better lifestyle choices.
"They can increase their level of physical activity or adopt a healthier diet.
"Both of these would minimise the risk of developing diabetes or heart disease."
Researchers don't know the cause of the increased obesity risk, but Derraik said further studies could shed light on the issue.
"It could be because the fetus is exposed to stress due to an abnormally long pregnancy or it could be due to the deterioration of the placenta that occurs late in pregnancy."
Genetics could also play a role, he said.
Researchers were unable to rule out the possibility that women born post-term were heavier in part because their mothers were heavier.
However, an earlier Liggins Institute study of children born post-term found similar effects when a mother's weight was factored into the results.
"We showed that children who were born post-term had more body fat and more abdominal fat, even after controlling for parents' BMI.
"And their bodies were less efficient at handling sugar. All of these are risk factors for type 2 diabetes and cardiovascular disease."
Girls born post-term were on average 1 kilogram heavier and had a higher body mass index than women born at 38-40 weeks.
"While the effect was relatively small, it's an important part of the puzzle in explaining how early experiences help programme our metabolism and set our likely weight-range as adults," Derraik said.
In New Zealand, an estimated two to three percent of all live births are post-term, while the rate varies from 0.4 per cent to 8.1 per cent in Europe.
In the past, post-term births accounted for more than 10 per cent of births, he said.
"Our findings are even more relevant for previous generations where there were greater rates of post-term births."
Liggins Institute and Uppsala University in Sweden looked at more than 200,000 Swedish women aged over 18 years for the combined study.
Researcher next plan to look at whether the same effect can be seen in baby boys who arrive late.