"We are a man, woman and child. It's ironic that we are so different but yet, we're just a family, just the same as anyone else," he said.
When asked why he makes many people uneasy, Beatie said, "I think that people are not used to seeing the image of a pregnant man. And it's causing a lot of people to think. … I used my female reproductive organs to become a father."
Thomas Beatie was born Tracy and grew up in Hawaii. A beautiful young girl, Beatie said he never felt particularly feminine growing up.
"I felt rough and tumbly," he said. "I didn't like frilly stuff."
In 1986, when Beatie was 12 years old, his mother committed suicide. He said his father pushed his tomboy daughter into becoming a model.
"Back then, I did not see an attractive young girl," he said. "Putting on makeup, I felt like I was putting on a costume."
At 14, he entered the Miss Teen Hawaii USA contest and became a finalist.
"I remember feeling uncomfortable on stage," he said.
Eventually, Beatie traded modeling and pageants for karate and the gym and began to dress like a man and use the men's bathroom. Although he had several boyfriends, he now says he hated sex.
At 24, Beatie began a lesbian relationship with Nancy, a bodybuilder, and moved in with her and her two daughters from a previous marriage.
In 1998, he decided to change genders. Psychological testing confirmed that he identified with being a male and he began to medically transform his body, first, by injecting the male hormone testosterone.
"My voice started to change," he said. "It started to crack like I was going through puberty. My bones felt stronger, my ligaments felt stronger. I started to grow facial hair."
In 2002, Thomas Beatie, still legally Tracy, had sex reassignment surgery to remove his breasts.
"That day was -- the most liberating day of my life," he said. "I literally felt like a weight was lifted from my chest."
To legally change genders is a long and complicated process. No federal law applies and state requirements vary.
In Hawaii, with a letter from a doctor certifying Beatie's psychological testing and irreversible surgery, he was legally allowed to change his birth certificate from female to male and his name from Tracy to Thomas.
Though Beatie physically and legally transformed himself from a woman to a man, he did not have "bottom" surgery, known as phalloplasty, to create an artificial penis. He also left his female reproductive organs in place.
"I don't feel like removing your sexual reproductive organs will make you any more of a man or any less of a woman," he said.
Last year on "20/20," Walters reported on how children as young as 5 years old are transitioning from one gender to another. And in the last few years transgender people have gained gradual acceptance, even showing up in Hollywood plot lines, such as on the TV series "Ugly Betty" and "Dirty Sexy Money."
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