I have heard of cases where the pregnant woman was pregnant on twins,at the sonagraph no foetus was seen,however it turned out the other twin was behind the empty sac...
I don't know if that is even possible,I'm just wondering could it have been possible that your mother was having twins?
One twin dies and is absorbed,leaves empty sac,and it might explain the low hormone levels?
I'm just throwing it out there,its an interesting case.
There is an expert on pregnancy on the board,perhaps she may be more helpful then I.
Or least,correct me if my limited knowledge is incorrect.
Edit: I did not explain myself properly in the first paragragh,but I hope you catch the drift of where I was going with it.

