Genetics/Blood Type

[swest at imt.net]

My daughter-in-law has AB Pos blood - my son has AB Neg.  She has suffered 
three near fatal miscarriages and has recently found out she is pregnant.  The 
Doctor in the town through which she had the last miscarriage told them it 
could be a genetic chromosone problem...like on the "leg" was missing from the 
 X or Y.  Her mother is B neg and her father was O Pos.  I am A Neg and 
took all the Rhogam shots many years ago.  Could anyone offer some information 
to this problem?  It would be most appreciated.  Please understand it needs to 
be in layman's language.  What genetic information from either side would be 
useful to us?

Many thanks beforehand
swest at imt.net