Creepy mother but good story
The narrator kept referring to Harry as "it" in your story, which is not typical of a woman like that. She is more likely to refer to the baby as "him" instead. Other from that. it is an interesting idea.
I really like this story as-is. I would definitly follow a longer AU, but the way it's written is almost poetry.
I'm of the other opinion. I love the way you left things hanging, questions unanswered, much like the Twilight Zone did to good effect. This piece sounded very much like a Rod Serling script to me.
This is an excellently written "what if?" story. I think it would be interesting if you did a chaptered piece following "Andrew" in this new situation.