Unless she tells you there is no way.
The hospital cannot provide you with that information. It's against the law. In any case, what you want to do is an invasion of your friend's privacy.
A person's medical history is protected by federal and state laws, and anyone trying to bypass such laws will find themselves in very serious trouble. It is indeed odd that someone would be concerned with another person's very private issues. Making accusations indeed prying into someone else's personal affairs often ends up in civil litigation, such things are better left alone.
ANSWER If you are really a friend, you wouldn't push the issue, being somebody who recently miscarried it did a lot of emotional damage, just be a friend and give them the benefit of the doubt. i don't know where i would be without my support system. but if you do find out she wasn't truthful... maybe suggest she get the help and attention she needs, because that is a horrible thing to lie about.