THE planned abortion of one healthy twin because the mother said she could not cope with two babies was "no different from any other abortion", the British Medical Association's head of ethics said yesterday.
Dr Vivienne Nathanson said the decision was bound to cause "instinctive horror" but insisted it raised no new ethical issues.
However, anti abortion campaigners attacked the procedure for the arbitrary nature of choosing which foetus would live.
Identified in a Sunday Express article as Miss B, the woman is a 28 year old single mother of one. She is 16 weeks pregnant with twins. The gynaecologist who agreed to perform the operation, Prof Phillip Bennett, said he offered the woman the option when she said she would choose abortion rather than give birth to both babies.
Prof Bennett of Queen Charlotte's Hospital, west London, said he and his team perform up to five such selective terminations every year. But to date all have been carried out in cases of in vitro fertilisation (IVF) where the foetus has shown signs of abnormality.
Prof Bennett described yesterday the ethical dilemma facing him in the case of terminating a healthy foetus as "playing God".
"I am not a murderer, not in the legal sense," he said. "But in a moral and emotional sense I am terminating a life.
"It's an interesting concept that once a baby is born we cannot kill it. But I'm not sure there is any difference with infanticide, other than that the law is different," he told the Sunday Express.
Prof Bennett indicated that, morally, he believes abortion is wrong. "Broadly speaking it is better not to interfere with life. I don't draw any major distinctions between embryos, foetuses and newborn babies in terms of existence."
The decision to terminate Miss B's foetus was taken in order not to risk the death of both foetuses. The killing of one healthy twin sounded unethical, Prof Bennett conceded, but he decided to proceed with the termination because it would be better to terminate one pregnancy as soon as possible and leave one alive rather than lose two babies.
It is understood that Prof Bennett is aware of the sex of both foetuses, but he would not say whether that information had been shared with Miss B.
The law in Britain currently allows the termination of pregnancies at 24 weeks; until recently the limit was 28 weeks.
However, Prof Bennett admitted he has performed a number of second and third trimester terminations.
On a "handful of occasions" he has terminated the pregnancies of women who were at the 40 week stage. He explained that legally a pregnancy can be terminated "right up to the moment of delivery" if the baby would be seriously handicapped.
Dr Jack Scarisbrick of Life, an anti abortion organisation, warned of future trauma for the surviving twin and said the decision to perform the operation demonstrated "the extent to which the medical profession has been brutalised".
Mr Paul Tully of the Society for the Protection of Unborn Children attacked the technique used in "selective termination". He said: "No other technique is quite so explicit in terms of killing the child. I would think doctors would be utterly averse to performing these procedures.
"And it highlights how abortion discriminates in an utterly arbitrary way against unborn children. Which of these twins is going to be killed and which will live?"
Dr Nathanson of the BMA said the act could be justified legally on medical grounds because multiple births did carry more risks, or social grounds if the woman could not cope with twins.