Babies are being born bigger

It’s official. Babies in New South Wales are getting bigger at birth. An in depth analysis of birth weight in babies born in NSW between 1990 and 2005, published in the Medical Journal of Australia, shows a significant increase in babies that weigh 4 kg or more at birth – such that almost 1 in 6 boys and 1 in 10 girls now weigh more than 4 kg.

The investigation examined records of around one million babies born in the 16-year study period.

Postdoctoral research fellow at the University of Sydney at Royal North Shore Hospital, Dr Ruth Hadfield (et al) said some factors had been identified as potential reasons for the increase in birth weight, such as the increasing rate of maternal diabetes.

High birth weight may have important adverse health implications for infants, contrary to the popular idea that big babies are healthy babies.

"For example, there is evidence of a relationship between high birth weight and the increased future risk of asthma, type 1 diabetes and a number of cancers, including infant and childhood leukaemia, and breast, prostate and colon cancer.

"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," Dr Hadfield said.

The research also shows that the reason for increasing birth weight in babies is largely unexplained.

"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 by our data.

"Further studies to ascertain all factors contributing to the increasing birth weight over time, including maternal pre-pregnancy body mass index and weight gain during pregnancy, are warranted."

(Source: University of Sydney: Medical Journal of Australia: April 2009)