The High Court in Dublin has ruled that doctors can give a blood transfusion to severely anaemic twin babies after they are born later this week.
The parents are Jehovah's Witnesses and refused to give their consent.
Doctors believe the babies are at risk of death or serious life-long disability and need to be delivered early.
They say the babies will need a blood transfusion in the minutes and weeks after their birth.
In a letter to Ms Justice Mary Laffoy, the mother, who is 32 weeks pregnant, said she and her husband loved their children with all their hearts and did not want to cause them harm.
However, she said they could not consent to the transfusion because of their long-held scriptural beliefs.
Jehovah's Witnesses' religious objection to blood transfusions stems from their interpretation of Bible verses that forbid Christians from ingesting blood.
She said she understood the seriousness of the situation and the fact that doctors feared there may be no other choice.
The mother said they would not interfere with the decision of the court, but asked for bloodless alternatives to be tried first.
Ms Justice Laffoy ruled that the doctors could give the transfusion if medically necessary and where no other alternative methods were available.
The court heard the situation arose because the mother refused an injection of a blood product, Anti-D, after the birth of her first child a number of years ago.
Anti-D is given where a mother with the Rhesus D negative blood group gives birth to a Rhesus D positive child.
If Anti-D is not given, the mother will develop antibodies against Rhesus D positive blood, which could affect future pregnancies.
In this case the twins are both Rhesus D positive and the mother's antibodies attacked their red blood cells.
The court also heard the normal management of foetal anaemia is to perform a blood transfusion in the womb, but the parents did not consent to this treatment.