No matter how much she shrieks don't get too close. You've heard of all the stories where kids get within the gorilla's reach and he bites into their arm - you have been warned.
You remember all the breathing exercises that you did with your loved one in the Lamaze classes. Now is the time to forget them. The last thing your wife wants to hear come out of your mouth as she hits a contraction is the word breath. She's way, way, way past that. Attempting to persuade their spouses to breath when their better half is planning the painful demise of the idiot who got her into this situation can be fatal.
Suggesting that "maybe it's just wind" will get you nowhere.
Leave the labor ward for a quick smoke
Mention the similarity to a scene from "Rosemary's Baby".
Tell her how nice the nurse is.
Ask for the remote so you can watch the game.
Remind her that she wanted a natural birth and was willing to deal with the pain.
Buy her curry and bean soup, no matter what she says.