The 25-year-old woman and her parents only found out last year they were not actually related after the daughter and mother donated blood.
They believe staff at LKH Graz likely made a mistake and switched two babies after they born, although the hospital say there is no evidence of malpractice.
Prosecutors publicised the case earlier this year and appealed for 200 women who were born around the same time - between October 15th and November 20th 1990 - in the same hospital to take DNA tests to see if they were switched at birth.
In seven months, only 30 of the women have come forward and taken DNA tests, with no further evidence of a switch found so far.
Both the 25-year-old and the parents who brought her up want to sue Steiermark Hospital Association (KAGes) for damages and, above all, to establish that the switch actually took place at LKH Graz.
According to their lawyer Gunther Ledolter, who wrote to KAGes two months ago, hospital bosses have not explicitly admitted that the switch took place in the hospital. Previously, they suggested it may have happened later on.
Ledolter did not confirm how much the family are seeking from the hospital, although media have speculated it could be as high as €255,000, or €85,000 each for the daughter, mother and father.
A spokesperson for LKH told ORF that an out-of-court settlement is at the moment not possible.
“The fact alone that the relevant person is not the birth daughter and that an unnoticed baby swap is likely to have taken place at birth, is not sufficient to accept that it was due to the actions of company employees,” the hospital said in a statement.
Meanwhile the mother has adopted the 25-year-old, who is unlikely now to meet her birth mother or father.