Cynthia Nixon's partner Christine Marinoni gave birth to the couple's first child together, a son called Max, yesterday (07.02.11).
Cynthia Nixon's fiancee has given birth to their son.
The representative said: "Christine and baby are doing great."
No further information has been given.
Cynthia, 44, has previously revealed how her kids Samantha, 14, and eight-year-old Charles - whose father is her former boyfriend Danny Mozes - are close to Christine and even call her mummy.
She said last year: "Maybe I'm just lucky, but I feel like Christine is so amazing with our kids - because they're our kids.
"I feel like falling in love with her is part of being amazed at how she makes our family so much better."
The actress also admitted one of the reasons why she loves Christine, 43, is her "butchness".
She said: "She's basically a short man with boobs. A lot of what I love about her is her butchness. I'm not saying I fell in love with her in a sexually neutral way. I love her sexuality - it's a big part of what I love about her - but I feel like it was her.
"It wasn't something In Me that was waiting to come out. It was like, this person is undeniable. How can I let this person walk by? Christine would probably kill me for saying this, but my daughter said one time that if you really had to break this down, it looks like she would be butch and I would be femme... but really once you get to know us it's really the opposite."
Cynthia and Christine started dating in 2004 and announced their engagement in 2009.