It was discovered last year that Alder Hey Hospital in Liverpool had stripped and retained organs from babies who had died there between 1988 and 1995.
Now it has become apparent that foetuses, mainly the result of births and terminations, have also been retained.
'No consent'
The 400 foetuses stored at Alder Hey were collected from many hospitals in the north west of England.
The vast majority - more than 300 - came from two maternity hospitals in Liverpool which merged to form the Liverpool Women's Hospital five years ago.
In the Alder Hey baby organ controversy, it emerged that hundreds of families were unaware that brains, hearts, and other organs had been retained from the bodies of their children who had died after surgery.
Pity2 says this the foetus collection was also made without the parents' knowledge or consent.
Liverpool Women's Hospital has confirmed that it sent 320 foetuses to Alder Hey as part of its routine pathology service.
It is believed the maternity hospital thought the foetuses would be sensitively and appropriately dealt with after any post mortem examination.
Ian Cohen, a solicitor representing the families, said: "If a mother has given consent for the hospital to dispose of a foetus in a humanitarian manner, then anybody would expect that those wishes are upheld.
"If it would appear that a whole foetus has been retained contrary to what was told to the mother then that is fundamentally wrong."
'Nothing new'
Hugh Lamont, a spokesman for the North West NHS Executive, said it was well known that the collection of organs at Alder Hey included foetuses.
He told the BBC: "The existence of foetuses at Alder Hey has been known about for at least 10 months, and representatives of Pity2 were briefed on this in July.
"It seems to me that this is yet another attempt to put the boot into Alder Hey.
"This story is not in the interest of bereaved families.
"It will be devastating for many people to wake up in the morning and hear what appears to be yet another shock horror revelation about Alder Hey when in fact in this case there is absolutely nothing new to be said."
However, Mr Lamont admitted that "the likelihood" was that consent was not sought from parents before foetuses were retained by the hospital.