The revelation follows the publication of a damning report into the baby ashes scandal and practices at Edinburgh's Mortonhall Crematorium.
Rules on collective cremations of foetuses in adult-sized coffins were relaxed in the code of practice drawn up by the Federation of Burial and Cremation Authorities (FBCA) in 2000.
Willie Reid, a parent and chairman of the Mortonhall Ashes Action Group, said he was shocked by the findings and repeated his calls for a public inquiry.
The report into the scandal recorded the former crematorium manager, George Bell, recalling foetal remains being brought from Edinburgh's Sick Kids hospital in little coffins.
He told the inquiry: "The FBCA code stated that there should only be one body cremated at one time."
But he said a bereavement counsellor at Edinburgh Royal Infirmary (ERI) later approached him on the instructions of the chief midwife and other senior managers about how to reduce costs.
Mr Bell said: "We were approached by NHS to carry out communal cremations, which we did. Rather than do it individually, they did it by the bulk. I need to emphasise that it was on their request.
"Staff accepted this practice because it was perfectly legal."
Fiona Mitchell, general manager of women's and children's services at NHS Lothian, said: "We are still considering the report as a whole."