Aussie baby weights climbing

Australian babies are becoming increasingly big bundles of joy, and health experts say that is not something to be happy about.

A decline in smoking during pregnancy - resulting in fewer low-birthweight babies - had occurred since 1990, showed a study that included almost 1.3 million births.

Mothers with gestational diabetes, resulting in heavier babies, also rose and these two factors contributed to a rising rate of newborns weighing more than 4kg.

The study, published in the Medical Journal of Australia, looked at babies born in New South Wales in the 16 years to 2005.

Dr Ruth Hadfield, who conducted the study with University of Sydney colleagues, said heavier babies had increased health risks, contrary to the popular notion that big babies were healthy babies.

"For example, there is evidence of a relationship between high birth weight and the increased future risk of asthma, type one diabetes and a number of cancers, including infant and childhood leukaemia, and breast, prostate and colon cancer," said Dr Hadfield, who is postdoctoral research fellow at the University of Sydney at Royal North Shore Hospital.

"As well as the potential for lifelong health consequences, higher birth weights may also result in injury to the infant and the mother at the time of delivery."

During the 16-year study period, newborn boys weighing more than 4kg increased 10.5 per cent.

For newborn girls, the figure was 15.2 per cent.

In 2005, one in six newborn boys and one in 10 newborn girls tipped the scales at over 4kg.

Another factor was that women were giving birth later in life.

"Although decreasing smoking, increasing maternal age and increasing gestational diabetes account for a portion of the increase, a larger portion of the increase remains unexplained."

- AAP