Babies are being born bigger across NSW, prompting a study that involves women with gestational diabetes following special low-GI diets.
Researchers from the University of Sydney and Royal Prince Alfred Hospital will investigate whether diabetic women on such diets have smaller birthweight babies.
Last month, a 6.52 kilogram baby boy, Cordell Hayman, was born to a Wollongong mother with gestational diabetes - and doctors warn big babies like Cordell are becoming more common.
The percentage of NSW babies born heavier than 4 kilograms has risen from 10.9 per cent in 1990 to 12.1 per cent in 2005, data collected from midwives and published in annual Mothers And Babies reports shows.
A statewide study by the Royal North Shore Hospital and University of Sydney researchers tracking NSW birthweights over the same period is expected to uncover a similar trend. The study will be published next month in the Medical Journal of Australia.
Bigger babies are at risk of metabolic disease such as diabetes, hypertension and fatty liver disease
RPA endocrinologist Dr Tania Markovic said gestational diabetes, which affects almost 5 per cent of pregnant women, was one reason for higher birthweights. It increased by 45 per cent in NSW between 1995 and 2005. Maternal obesity was the main reason why Dr Markovic was treating more and more women with gestational diabetes.
She and researchers including University of Sydney professor Jennie Brand-Miller will monitor diabetic women on low GI-diets over a two-year period and measure their babies' body fat, as well as health.
"We know that bigger babies are at risk of metabolic disease such as diabetes, hypertension and fatty liver disease," Dr Markovic said.
Dr Danny Challis, clinical director of Obstetrics and Fetal Maternal Medicine at the Royal Hospital for Women, said birthweights had increased during his 20 years at the hospital. He said large babies resulted in delivery complications such as shoulder dystocia, where the shoulders of the baby get stuck during birth, which can cause injury and death. Large babies also resulted in more caesarean deliveries, he said.
Kerrie Barry - mother of Cordell - knew she was going to have a big baby when her partner, Glenn Hayman, measured her girth circumference at 140 centimetres.
An ultrasound at 35 weeks gestation estimated her baby was already a whopping 6.1 kilograms. Cordell was delivered by scheduled caesarean last month at 36 weeks, weighing 6.52 kilograms - almost double the average birthweight in Australia [3.37 kilograms].
Ms Barry had gestational diabetes, which was diagnosed early in the pregnancy, and she had twice-daily insulin injections. Her daughter, Bree, 4, weighed almost 5 kilograms at birth. Cordell is now home from Wollongong Hospital and is "pretty placid", according to his mum. He wears clothes to fit a three-month-old baby and wears crawler nappies.
> Average birthweight of live-born babies in Australia: 3.37kg (Source: 2008 Mothers And Babies Report).
> World's heaviest surviving newborn: 10.2kg boy, born in 1955 in Italy.
> Heaviest girl in recent years: 7.75kg, born in 2007 in Russia.
> Heaviest boy in recent years: 7.57kg, born in 2005 in Salvador, Brazil.