AUSTRALIAN researchers say they are "tantalisingly close" to proving a link between women who smoke during pregnancy and cancers such as leukaemia in their children.
Previous studies have found only weak evidence or even a reverse trend, with less cancer among the children of smokers.
But a new study links low birth weight, premature birth and newborn admission to intensive care -- all more common in the children of smokers -- with as much as a five-fold increase in childhood cancer.
In Victoria, almost one in 10 pregnant women smoke in the month prior to birth -- about half the number who were smokers when they first became pregnant.
The research, by the Cancer Institute of NSW, was presented at an international conference late last year and publicly released yesterday.
It came from an analysis of 1 million birth records in NSW, including more than 900 cases of childhood cancer.
Institute chief executive Professor Jim Bishop said it was the first time that a link had been shown between childhood complications such as premature birth and the risk of cancer.
The study found that babies born with a low birth weight had 1.7 times the risk of developing leukaemia.
Those born prematurely were twice as likely to be diagnosed with cancer.
Babies admitted to a neonatal intensive care unit were 2.7 times more likely to be subsequently diagnosed with cancer, and five times more likely to get kidney cancer.
Premature birth, low birth weight and admission to a neonatal intensive care unit were all strongly associated with a mother smoking during pregnancy.
The data was not strong enough to prove a direct link between smoking and childhood cancer. In fact, the raw data showed the reverse effect: cancer was slightly less prevalent among the children of smokers.
But Professor Bishop said that result was not statistically significant, while the other results were much more reliable.
"The link to smoking is tantalising, but it needs to be further investigated," Professor Bishop said.
"We anticipate having a larger data set within a year or two, and we'll be focusing on better quality smoking data."
Quit Victoria welcomed the research. Program manager Luke Atkin said it would add to the evidence that smoking during pregnancy was harmful to children.
"Pregnant women often think that the impact of smoking will just be lower birth weight," he said. "But it is also linked to reduced lung function and increased prevalence of asthma."
Victoria's new tobacco control strategy, released late last year, will specifically target pregnant women smokers with support programs and warnings.
