New scientific research has proved that it is possible for cancer cells to be passed from a pregnant woman to her unborn child.
This is the first time scientists say they have proved beyond doubt that the cells can be transmitted in this way.
The case they looked at was in Japan, where they found that leukaemic cells were passed from a woman to her unborn daughter.
Dr Frederick van Delft is a member of the research team from the British Institute for Cancer Research. He said cases like this were ''very rare''.
Dr van Delft said the placenta and the child's immune system were supposed to be able to prevent the cancer cells from being passed on but they occasionally failed.
Speaking to Newshour, he emphasised that this was the first time they were able to show genetically that this had happened.
First broadcast 13 October 2009
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.