How often do birth mothers change their minds?

I asked my agency case worker the same question. She said of the 100 adoptions they did lasy year in Guatemala, 5 of them changed their minds and all 5 did so at the DNA testing. To me this makes sense that if they did change their mind it would be at this step because they see each other when the DNA is taken and a picture is taken. It is my understanding that the birth mother signs off to relinquish her rights 4 times in the process. First when she leaves the baby, second when the DNA test is done, third when the social workers interview is done and finally when the case is out of PGN. Hope this helps.