Smoking when pregnant has long been frowned upon, but now a new study has revealed how cigarettes can damage the developing liver cells of unborn babies. The team of scientists, led by the University of Edinburgh, found that the deadly cocktail of chemicals found in cigarettes is particularly harmful to developing liver cells. Furthermore, they discovered that cigarette chemicals affect male and female foetuses differently, with male tissue showing liver scarring and female tissue showing more damage to cell metabolism. Using embryonic stem cells, the team developed a way of testing how maternal smoking affects liver tissue. They used pluripotent stem cells - cells that have the ability to transform into other cell types - to build foetal liver tissue. They then exposed said tissue to the harmful chemicals found in cigarettes – in particular, the specific substances known to circulate in foetuses when mothers smoke. 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."