How would you react if your teenage son or daughter told you that they was having a baby ?

I'd have to accept it and probably ask what they want to do about the future.  

I see my son naked occasionally and I know he's can't get pregnant. 

yes , if you can afford it why not , after all they where pregnant younger than you 200 years ago . Hope you enjoyed getting pregnant ..

Calmly let them know i’m furious, that they should walk away right now so i don’t kill them and then take enough time to actually calm down and really talk about it and find a way to work it out.

Start helping them by answering any questions, tell him/her that as a dad I've been there before and help them as much as possible.

I would pack their bags to get them ready to make it on their own in the real world.  I wouldn't turn my back on them, but would end childhood and all they take for granted.

Most parents I know (including my own) would react to this news by tossing you out of the house on your a** for being so dammed irresponsible. If you were male, they'd probably want to press charges against you for sleeping with their daughter.

You asked, I answered.

son............it would be historic

I would say good luck with that and tell them they can't live here

Start planning for life because they have to finish high school or they will most likely be destitute for life.  Figure out what the father plans on doing about it too.  Things will work out.