Will a foetus change the carrier's DNA?

We put the question to Kat Arney.

Kat - The simple answer is yes. The more complex answer is to look at why. Basically, there's a barrier between the mother's blood and the baby's blood which is the placenta, but stuff can kind of get across it and this is very interesting because there's evidence that bits of DNA from a foetus can get into the mother's blood. This is actually starting a very interesting area of testing maternal blood for the presence of for example, genetic defects in the foetus which could potentially be really useful because to look for things like down syndrome and things like that, you have to take a sample from the womb. That can have an increased risk of miscarriage. To be able to do these kind of blood tests, it could potentially be very useful. So yes, DNA from a foetus can get into the bloodstream of the mother. Potentially, also cells as well could be traveling around in the mother's bloodstream. Now, does it matter? Does it make a difference? Probably, not. The biggest risk to a mother from the foetus is probably from things like immune reactions and things like that from molecules produced by the foetus. They can be sort of blood group incompatibilities and things like that. But we do know for example that there are many, many, many successful IVF pregnancies that are done with donor eggs. This is women carrying babies that they have no relation to and they don't seem to have any ill effects on them or their children.

Chris - I think there's some suggestion that people who have been pregnant are much more prone to having autoimmune conditions where the immune system turns on itself or on the body itself. One suggestion is that this may be because there are cells from the baby lurking in those tissues from when the mother was pregnant. When the mother is pregnant there's a degree of immune "switch off" or immunosuppression to avoid the mother's immune system attacking what is 50 per cent genetically not her, because 50 per cent of the baby is obviously the dad's DNA. But once the pregnancy is over, then you've got this tissue there which is not the mother and then it turns on it in some cases and you get things like arthritis, thyroid disease, or maybe SLE - lupus.