That was debunked during one of her talks with Kay (cursed with seeing others' sins). She does indeed collect the one drop of blood from the newborns, but it's a red herring. She flushes it down the toilet.
She apparently invests in something 'out in the Mundy' that kills far more children than she ever did on her own, but is legal. It was implied that whatever it is would be thought of as utterly distateful by Fable 'values'.