Born female, he had his first sexual reassignment surgery to become a man in 2002, but four years ago, Thomas used his still functional ovaries to conceive via a sperm donor.
He became a hit on the Oprah Winfrey Show when he went public with his story, and made history when his daughter Susan was born.
He has since given birth to sons Austin and Jensen - but Beatie has decided three kids are enough.
He tells In Touch magazine, "I'm 99 per cent sure I won't have another child. I've always wanted a big family, but I'm very happy and fulfilled."
Beatie also tells the publication that doctors have advised against him having another child.
The pregnant man is now dating single mother Amber Nicholas, 42, after splitting from his wife Nancy.