A little info, because I think GWB is a pathological liar: I found an article from 1999 that recounts the events of his mother's miscarriage in a much more mundane manner. It's a long article, so I'm pasting the relevant portion below. That said, his mother was pro-choice, as was GHWB before he needed to conform to the neocon platform. Also, a claification: GWB was seven when his sister died. She was three, and died of leukemia.
Here's the excerpt from the article:
Once, in the mid-1960s in Houston, when his father was out of town, he drove his mother to the hospital when she was having a miscarriage.
Halfway there, Barbara Bush told her son, "I don't think I'll be able to get out of the car."
"I'll take you to the emergency room, don't worry," her son assured her.
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson