MS Roisin McAliskey, who is on remand fighting extradition to Germany in connection with the IRA bombing of a British army base in Osnabruck, was transferred to Holloway Women's Prison yesterday.
She had earlier experienced stomach pains in Belmarsh prison and was taken to hospital.
In a statement last night the Prison Service confirmed the transfer of Ms McAliskey, who is pregnant.
A spokesman said: "Throughout her time in custody Ms, McAliskey has received regular, medical attention."
The statement said she was in "good general health and her pregnancy is progressing normally. There are no special medical concerns at present but as a precaution following stomach pains, Ms McAliskey was taken to a locale hospital. As a further precaution she has been returned to Holloway Prison where special antenatal care is more readily available should it become necessary."
Earlier this week Ms McAliskey, who is also suffering from weight loss and asthma, had been transferred to the high security Belmarsh from Holloway.
It is understood that her mother, Ms Bernadette McAliskey, was denied access to her daughter by prison officers at Belmarsh.
Ms McAliskey's solicitor, Ms Gareth Peirce, said the "sudden and deliberate" transfers were "hardly accidental and were deliberate by design". Ms Peirce said Ms McAliskey's family had been prevented from visiting her by the transfers between prisons.
"She is a sick, pregnant woman, who was violently ill while travelling to court. The situation is beyond belief and it can't be accidental," she said.
At a press conference in the House of Commons, Mr Eamon O Cuiv, Fianna Fail's spokesman on prisoners' issues, who had also tried to visit Ms McAliskey, said he would be making a "very, very strong protest" to the Department of Foreign Affairs and would "ask the Tanaiste to take this up", following the "studied effort to block me" by the governor of Belmarsh Prison.
Mr O Cuiv, who has been visiting Irish prisoners in Britain, said, he was particularly concerned at the number of republican prisoners held in Special Secure Units.