Surgeons at Birmingham Women's Hospital are set to try and save the life today of a twin being slowly drained of life by its sibling in the womb.
Sarah Garrett has had to make the agonising decision to let doctors end the life of the abnormal twin - which grows and moves but has no organs - to boost the chances of survival of the healthy child.
Mrs Garrett, a child-minder from Mansfield, Notts, has an incredibly rare condition called 'twin reversed arterial perfusion syndrome', known as Trap.
It means that one of the foetuses has no head, arms or functioning organs yet is growing and kicking in her womb fed by the blood of its identical twin.
The condition affects one in every 35,000 identical sets of twins.
Mrs Garratt is hoping a procedure can be performed at the Women's Hospital to stop the blood circulation between the two twins.
"The way we've coped is by keeping hold of the fact that the other one is the normal baby," she said.
"It has been an incredibly lonely experience. I've gone through every feeling it's possible to feel. I still feel protective of the abnormal twin because it is inside me. But I have to do everything I can to help the healthy twin survive."
Mrs Garratt first learned of her condition at 12 weeks when she was given a letter from her local hospital to take to a specialist.
The pregnancy was unplanned. First she had been told she was pregnant with one baby, then with twins but that one of them had died.
"Curiosity got the better of me. I opened the envelope and it said '? Trap'. I looked it up on the internet.
"The images I saw were the surreal; ones you would get out of a horror movie. It took a minute when the images first started coming up. I had to sit back and think, this is real; it's inside me.
"It was very surreal and very strange to comprehend that is going on inside me. My husband and I spent a week in shock."
A scan at Queens Medical Centre in Nottingham proved the internet images accurate.
Letting the pregnancy continue puts the healthy twin at risk from heart failure because of the strain of pumping blood for both babies. But the surgery could cause the healthy baby to miscarry.
"It isn't straightforward," said mother-of-three Sarah, now four months pregnant.
At Birmingham Women's Hospital, surgeons will insert tiny surgical implements guided by a miniature camera lens attached to a fibre-optic cable through needle-sized holes in her stomach.
If the surgery is successful, the healthy baby will have an 80 per cent chance of survival and a 50:50 chance of being born without a heart defect or other disability.
"We are trying to cross one bridge at a time. We have to know that we have done everything we can to keep this baby alive," she added.