It would be inhumane to force a pregnant teenager to carry her baby for nine months knowing it would die, the High Court was told today.

The 17-year-old girl, known only as Miss D and from Leinster, is asking judges to allow her to travel to the United Kingdom for an abortion.

The teenager is four months pregnant, and last week she found out the foetus has not formed properly and suffers from anencephaly, meaning a major part of the brain, scalp and skull is missing. The newborn baby will live three days at most.

Miss D has been in the care of the Health Service Executive (HSE) since March and it asked gardaí to step in and prevent her from travelling. The court heard gardaí do not have those powers.

Opening the case, Eoghan Fitzsimons SC, for Miss D, told the court the diagnosis was most distressing for her. He said the HSE's claim that under law she cannot travel would require her to carry the baby full term only for it to die. He said that would subject her to degrading treatment.

"It seems here to be most inhumane to expect her to do that," he told the court. Mr Fitzsimons said Miss D would suffer mental and physical trauma and great discomfort, and he rejected claims made by a social worker that she had changed her mind about the abortion.

He insisted Miss D only accepted she would continue with the pregnancy if she lost the court battle. The girl's mother and her boyfriend support her decision to terminate the pregnancy.

Abortion is only allowed when there is a real risk to the life of the mother, including suicide. But Miss D has insisted she is not suicidal.

The court heard most women who discover their baby has anencephaly decide to abort the foetus, even in late stages of pregnancy.

Outlining more than a dozen reasons Miss D should be allowed to travel, Mr Fitzsimons said the HSE had misconstrued the meaning of the Children's Act. Mr Fitzsimons went on to document medical studies that showed complications from anencephaly and a risk to the life of mothers in these cases.

He also told the court that if Miss D was not in the care of the HSE and her parents supported her decision for abortion, there was nothing to stop her travelling.

The court also heard today that Miss D believed she should have the right to choose abortion. During a psychiatric assessment the girl told a doctor: "It's my body and I should be allowed to do with it what I want."

The psychiatrist's report noted Miss D felt guilty as she had not taken folic acid in the run up to her pregnancy or in its early stages. Reading an affidavit from Miss D, Mr Fitzsimons told the court: "She's being denied rights guaranteed to every citizen because she is under 18 and subject to a care order.

"It is discrimination of the highest order."

During the day-long hearing a medical report of an ultrasound which discovered the foetus was not developing properly was read out. Miss D, accompanied by her boyfriend, hurried from the courtroom as her lawyers went through it.

The court also heard the Children's Act, which Miss D is under, does not have the power to prevent her travelling.

Neither does it give the HSE the power to ask the gardai to stop Miss D leaving. An affidavit from the girl's mother, known as Miss A, was also read out claiming a social worker warned her the HSE was acting in loco parentis.

On top of that the HSE advised the mother her daughter was not allowed to leave the state and that a court case would end up in a media circus. The social worker did not tell the girl's mother gardai had been notified, the court heard.

Mr Fitzsimons added that the HSE did not have the power to act for Miss D's parents. The hearing resumes again tomorrow when the teenager's mother will insist she has the final say on whether she can travel. The court has already heard the mother fully supports her decision to have an abortion. The case continues.