The parents of conjoined twins are fighting a court ruling that the infants be separated — an operation that will save one baby but kill her sister.

Doctors say unless the girls are separated, both will die within three to six months. The infants, a pair of what is more commonly known as Siamese twins, are joined at the waist and share a heart and lungs. By the nature of their condition, only one could survive the operation.

The twins, known as Jodie and Mary (fictitious names assigned by the court to protect their identities), were born four weeks ago at Saint Mary’s hospital in Manchester, northwest England.

Conjoined twins are rare. The condition occurs once in every 50,000 to 100,000 births.

Jodie is the stronger of the two, and her heart and lungs support Mary. Doctors say the operation is Jodie’s only chance of surviving, as her organs can only support her sister’s body for a few more months.

The parents, devout Roman Catholics, say it is morally and legally wrong to sacrifice one child for the other and oppose the operation.

Doctors are challenging their decision, claiming inaction means death for both girls.

The case is making its way through the British courts as doctors, judges, ethicists, priests and parents struggle with the questions of right and wrong, life and death.

Last month, a judge ruled the operation should proceed. The parents on Monday asked the Court of Appeal in London to overturn the decision.

难点词汇：
　　　conjoin　 (使)结合　　　　Siamese　 暹罗人　　　　fictitious　 编造的
　　　devout 　 虔敬的　　　　　inaction　无行动　　　　ethicists　　伦理学家