The impact of cigarette damage to unborn babies has been revealed in a new stem cell study.
A University of Edinburgh-led research team has developed a way to monitor the long-term effects on liver tissue of pregnant mothers smoking using embryonic stem cells.
Chemicals found in cigarette smoke have been shown to damage foetal liver cells, but they affect boys and girls differently.
Dr David Hay, from the University of Edinburgh's Centre for Regenerative Medicine, said: "Cigarette smoke is known to have damaging effects on the foetus, yet we lack appropriate tools to study this in a very detailed way.
"This new approach means that we now have sources of renewable tissue that will enable us to understand the cellular effect of cigarettes on the unborn foetus."
The liver is vital in clearing toxic substances and plays a major role in regulating metabolism.
Smoking cigarettes, which contain around 7,000 chemicals, can damage foetal organs and may do lasting harm.
Scientists used pluripotent stem cells - non-specialised cells with the distinctive ability to transform into other cell types - to build foetal liver tissue.
These were exposed to harmful chemicals found in cigarettes, including specific substances known to circulate in foetuses when mothers smoke.
The study showed a chemical cocktail similar to that found in cigarettes harmed foetal liver health more than individual components.
Findings also showed the chemicals damage the liver differently in male and female foetuses, with male tissue showing liver scarring and female tissue showing more damage to cell metabolism.
The study was carried out in collaboration with the Universities of Aberdeen and Glasgow and is published in the journal Archives of Toxicology.
Professor Paul Fowler, director of the Institute of Medical Sciences at the University of Aberdeen, said: "This work is part of an ongoing project to understand how cigarette smoking by pregnant mothers has harmful effects on the developing foetus.
"These findings shed light on fundamental differences in damage between male and female foetuses."