Pregnant smokers pass on carcinogens to babies

SCIENTISTS HAVE uncovered the first direct evidence that women who smoke during pregnancy can transfer cancer-causing chemicals to their unborn babies.

A study of smoking women has shown that the first urine samples collected from their newborn babies contain significant quantities of potentially dangerous carcinogens found only in tobacco smoke.

The researchers who carried out the work believe the findings suggest that babies born to smoking mothers may be at risk of developing cancer in later life as well as becoming predisposed to nicotine addiction while still in the womb.

Although doctors strongly advise smokers to stop during pregnancy, more than six out of 10 continue to smoke. The latest findings suggest that some childhood cancers might be the result of exposure to tobacco carcinogens in the womb.

Professor Stephen Hecht, who led the investigation at the University of Minnesota in Minneapolis, said the results are the first to prove that exposure to cancer-causing substances in tobacco can occur before birth.

``It is the first evidence for the presence in the foetus of a transplacental carcinogen [passed from the mother] derived from tobacco smoke. There are no previous reports of carcinogens in the urine of newborns,'' Professor Hecht said yesterday. The study monitored 48 smoking and non-smoking women. Doctors analysed urine samples from their newborn babies for the presence of a substance called NNK - a strongly carcinogenic chemical derived from nicotine.

Professor Hecht said that NNK has been shown to cause cancer in a range of laboratory animals and is likely to be one of the main causes of lung cancer in smokers.

Experiments have also shown than NNK can pass from pregnant animals to their unborn offspring, which are significantly more likely to develop tumours in later life.

Professor Hecht said he detected the breakdown products of NNK in the urine of 22 babies born to the 31 women in the study who had smoked during pregnancy. By contrast he found no trace of NNK in any of the 17 women who did not smoke.

The amounts of NNK in the babies were about a tenth of those found in adult smokers. ``The levels measured are substantial when one considers that exposure of the developing foetus to NNK would have taken place throughout pregnancy,'' Professor Hecht said.

The scientists also found nicotine and cotinine - a breakdown product of nicotine - in the urine of the newborn infants. ``The exposure to nicotine and cotinine in newborns is substantial, leading one to wonder whether a pattern of nicotine addiction could begin before birth,'' Professor Hecht said.

Epidemiologists have failed to find a definite link between smoking mothers and cancer in children but the latest study suggests one might be found with further research.