The Caesarean took place on Monday but the case was only made public yesterday. The condition of the mother, described as a born-again Christian and referred to in court only as Mrs S, was said to be serious.
It is thought to be the first time such a case has come to court, although a similar instance is said to have occurred last summer. On that occasion, the judge was told, crisis was averted.
Sir Stephen Brown, president of the Family Division, authorised the London health authority to carry out the life-saving operation after hearing from a surgeon that the plight of the woman, aged 30 and a mother of two, and that of her unborn child was 'desperately serious'.
He added: 'The evidence of the surgeon is that we are concerned with minutes rather than hours and that it is a life and death situation.'
Mrs S was admitted to hospital last Saturday with labour complications. Her baby's birth had been predicted for 6 October.
The judge said doctors had done their best to persuade the woman that the only means of saving her life and that of her child was to carry out a Caesarean section. Her refusal to have the operation was supported by her husband.
'The surgeon is emphatic. He says it is absolutely the case that the baby cannot be born alive if a Caesarean operation is not carried out,' Sir Stephen said.
Medical experts said yesterday it was unlikely the case would increase the likelihood of doctors overriding patients' wishes if the situation recurred. Both the British Medical Association and the Medical Defence Union said any new case would have to be tested in court.
Dr Graham Burt, of the MDU's medical division, said: 'It is not a situation where legal precedent would apply. It may be that one could use the case in discussions with patients who were reluctant to agree, but each invididual case is very different.'
However, there was mystification over what religious belief, apart from an intense commitment to 'faith' over technology, could have prompted the woman's refusal. The nature of her objections was not made clear.
Phyllis Bowman, national director of the Society for the Protection of the Unborn Child, who praised the court's decision, said: 'I cannot think what objections the woman could have raised towards having the operation. We have born-again Christians who are members of our organisation and I know of nothing in the bible which would be against such an operation.'
The Jehovah's Witnesses, who refuse blood transfusions because they regard them as bad medicine, have no objections in principle to Caesarean section.
However, a spokesman said that an individual Jehovah's Witness might have a personal objection. Neither the hospital nor the family can be identified.
Law report, page 26