Megan Fox gave birth to her son Noah in September and revealed on Monday how painful the labor process was.  

The "This is 40" acterss told Access Hollywood's Shaun Robinson at the film junket for her new movie that her water broke in the car ride to the hospital with her husband Austin Green. 

"I was screaming for an epidural when [Brian] was driving me to the hospital because my water broke on its own and I was immediately -- it was level orange alert pain," Fox said.

"It hurts so bad," she continued. "It was so intense. And I thought I was gonna be really tough and make it, I was gonna labor to like 8 cm... but the first contraction that I got was horrific!"

"This is 40," starring Paul Rudd and Leslie Mann, opens on Dec. 21.

Fox recently hired a night nurse two nights a week to help her and her "90210" actor husband. The 26-year-old married Green in Hawaii in 2010. The actor has a son named Kash, 10, from a previous relationship. Fox was named The Sexiest Woman in The World in 2008 and is well-known as being Shia LaBeouf's high school crush and then girlfriend in the first two "Transformers" film. However, she said she is more cautious about exuding sex appeal in her acting roles now that she is a mother. The actress will choose film roles more carefully, which means she will be showing less skin than in the past. 

"It changes your perspective about being overly sexual in a film when you have a baby," she said. "I'm going to be more cautious about choosing films because I'm already thinking about when he's in school and his friends are going to be showing him my photo shoots with me in a bikini and he's going to be horrified.

"So that will deter me from making some of the choices I made before."

Tags: Megan Fox this is 40 austin green