"The fiddliest thing" ... Kellie Bush watches on an ultrasound screen as her unborn child receives another blood transfusion.

"The fiddliest thing" ... Kellie Bush watches on an ultrasound screen as her unborn child receives another blood transfusion. Photo: Anthony Johnson

A blood transfusion is never without risks. When it is for an unborn baby the stakes are even higher.

It is a procedure that the NSW Foetal Therapy Centre, at the Royal Hospital for Women, performs only about half a dozen times a year. The death rate is 2 per cent.

Despite the anxiety for her child, 31-weeks-pregnant Kellie Bush agreed to allow The Sun-Herald to record the rarely witnessed process in theatre.

Ms Bush's blood group is rhesus negative but that of her unborn baby is rhesus positive.

Her defence mechanism assumes the baby's blood is alien and produces antibodies to fight it, resulting in the baby becoming anaemic. Drugs that can sometimes overrule antibodies did not work in her case. Without intervention Ms Bush's baby would probably not have got this far.

Alec Welsh, professor of maternal foetal medicine at the University of NSW, used a fine needle to inject 90 millilitres of donated blood into a vein in the baby's liver, with an ultrasound screen in the darkened theatre to guide him. There was a big risk each time, Professor Welsh said.

''The antibodies are trying to destroy the baby's blood cells. With a foetal blood transfusion there is a 2 per cent loss rate with bleeding inside the baby,'' he said.

''It's about the fiddliest thing we do just lining things up. The last thing you need is for the baby to do a somersault.''

Finding a matching donor is also a challenge - it was planned for last week and blood was located in Victoria but then the transfusion was postponed. In NSW there are only eight suitable donors.

It was the third transfusion during the pregnancy for Ms Bush from Gosford, whose husband Paul was by her side.

The couple already have two girls, Charli, 4, and Eden, 2 - who also needed transfusions.

Ms Bush, still connected to a monitor after the half-hour procedure, managed to stay relaxed and smiling throughout.

''I was told that if the baby gets anaemic it will move less but [it] just seems to do cartwheels every day all day,'' she said.

Asked if she was planning to add further to the family the answer came without hesitation.

''No. We had no more planned after Eden. This is a little surprise.''