At my scan today.. she said I have a low lying placenta at 24-25mm and need an extra scan to see if…

At my scan today.. she said I have a low lying placenta at 24-25mm and need an extra scan to see if it goes to 30mm which I can understand ... BUT what in the world is this low PAPP-A? I can’t get my head around it ? she actually said mine is ok but it’s on the cusp so they are just checking to make sure but I have no idea lol 😆...