Wynne - get a paternity test, and then sue for custody.
If you don't get the test, and the kids is not yours, the state doesn't care and will go after whomever is on the birth certificate for child support - might hear this referred to as "providing male".
If the kid is confirmed to be yours, you're going to have to sue for custody.
You're not going to be able to do the test until the kids is born though, so maybe just give her some space for a moment, it could be her freaking out about being pregnant. Don't let her burn bridges. I'd definitely say "okay, i will" next time the paternity test is brought up, and see how she reacts.