Question about statutory rape?

Okay, say there is this guy who is 21 and he is at a party. A 17 year old girl appears and they start to hang out. The girl tells the man that she is 19 which is a legal age. They end up having sex. Weeks later she ends up getting pregnant and starts crying out rape. What would happen to the guy? Would the girl get in trouble? how would they go about punishing people? What would the punishments be? What would happen to the baby? How would they make a verdict? What kind of eviedence would there have to be to make a desicion, or do they just believe everything she says and just put him in jail.