Smoking while pregnant may damage the genetic material of foetal cells, and increase the risk of cancer in later life, research suggests.
Smoking in pregnancy is not advised
Smoking in pregnancy has been linked to problems such as growth retardation, and obstetric complications.
But the latest research by the Universitat Autonoma de Barcelona suggests it also triggers abnormalities in foetal cell chromosomes.
Details are published in the Journal of the American Medical Association.
The Barcelona team examined the effect of maternal smoking on cells produced by the foetus which break off and float around in the amniotic fluid which surrounds it.
These cells - foetal amnioctyes - were obtained during routine amniocentesis tests.
The researchers compared cells taken from 25 smokers, and 25 women who did not smoke during pregnancy.
They found cells from foetuses whose mothers smoked during pregnancy showed higher levels of chromosomal abnormalities, damage and instability.
Further analysis showed that a chromosomal region previously linked to the development of blood cancers was most affected by tobacco.
The researchers say their findings raise the possibility that smoking during pregnancy may put children at risk of developing cancer later in life.
In a commentary piece published in the same journal, Dr David DeMarini and Dr Julian Preston, from the US Environmental Protection Agency, say other research has hinted that tobacco smoke can mutate the genetic material of the developing foetus.
However, they point out that the latest study has its flaws. For instance, no scientific measure was made of the level to which each foetus was exposed to tobacco.
More work is required before definitive conclusions can be drawn, they write.
"In the meantime, the message to women based on the published literature remains clear: smoking during pregnancy can be hazardous for both the foetus and the mother."
More work needed
Professor Gordon Smith, and expert in obstetrics and gynaecology at Cambridge University, told the BBC News website he could think of no previous evidence of a strong association between maternal smoking and foetal abnormalities.
A study of over 600 cases of childhood lymphatic leukaemia, for instance, found no evidence that cancer was more common among children whose mothers smoked during pregnancy. Professor Smith said: "We know that maternal smoking is harmful to the offspring for many reasons.
"This study adds another mechanism by which maternal smoking might mediate its harmful effects.
"But it will require further work to understand whether this biological effect of smoking adversely affects the health of the offspring and what proportion of adverse outcome in the offspring is explained by this mechanism.
"It should certainly lead to studies of the long term outcome of the children of smokers."