California is soon to begin issuing $250 million in bonds to finance the institute, which has been surviving on loans and private donations while it battled lawsuits with its disgruntled opponents. In this uncertain environment management of the CIRM has proved difficult and several top executives and scientists have left in recent months. But the CIRM board is confident that Dr Trounson will make up for lost time.

The fertility clinic admits that the woman mentioned on the day that she wanted only one embryo to be implanted, but points out that she had signed a pre-admission form in which she consented to one or two.

The woman and her partner allege that the twin pregnancy jeopardised their careers, their relationship and their health. They also had to scrap plans for a trip to England. The mother suffered pre- and post-natal depression and could only work a few hours at a time because of the pain. The couple needed relationship counselling for about 18 months.

One solution would have been foetal reduction, but that would have put the other child at risk. Another was adoption, but that would have been too emotionally wrenching for the women.

• Act with skill and care, keep skills up to date
• Prevent corrupt practice and declare conflicts of interest
• Respect and acknowledge the work of other scientists
• Ensure that research is justified and lawful
• Minimise impacts on people, animals and the environment
• Discuss issues science raises for society
• Do not mislead; present evidence honestly

An official spokesman, Father Augustine Di Noia, explained that "What we're seeing here is that the quality of life is not a judgment that is in our hands to make. Life is a gift from God, and the Church has consistently taught that it is a gift that is not subject to the determination and decision of anyone, including the person himself or herself who is ill."

Father Di Noia contended that the human person has a "dignity which perdures through all of the various physical states which each person experiences in life from the existence in the womb to the final moments before death. At no point can life be terminated for any reason."

However, Dr Robert Lanza, of Advanced Cell Technology, an American company which has been working on hybrid embryos for some time, says that his efforts to do this have been unsuccessful when two species were quite different. "They grow to the 16-cell stage, then just before going on to become blastocysts, they block," he told New Scientist. He suspects that this happens because the animal mitochondria in the cytoplasm stops communicating with the human genetic material.

The president of the Association of Organ Procurement Organizations (OPOs), Thomas Mone, insists that this case was an aberration. However, doctors, nurses, and others say that they have noticed a growing pressure to supply organs since 2003, when the Federal government launched a campaign to maximise the supply of organs from deceased donors. The employees of the OPOs work with hospitals to identify potential donors.

Some bioethicists are critical of how the OPOs work. "It's like they're vultures flying around the hospitals hovering over beds waiting for them to die so they can grab the organs," says Michael Grodin, of Boston University.

And bioethicist Daniel O. Dugan told the Washington Post: "In some places, the organ-procurement folks will actually go into the room and meet the family and wear scrubs that are the same colour as the hospital personnel and allow themselves to be experienced by the family as being members of the hospital staff... They will introduce themselves and build a kind of rapport when actually their whole agenda is organ procurement."