It's getting late for that route at 4 months.I don't know how far along she is, but it seems most people assume they are keeping the baby.
Maybe he's trying to get her somewhere for her to abort. Whether per her wishes (and against the parents') or his, or both.
When she was reported missing it was said she was 3 months.
There's also the expense and state's strict abortion laws.
Unless they're in Mexico.