The actress, who is Jewish, told The New York Times: "I'll be showing soon". But I'm married to Daniel.
Weisz went on to say, "We're going to have a little human. It's all such a mystery!"
Rachel is a mum to 11-year-old Henry, who she welcomed with Hollywood director Darren Aronofsky while the pair dated between 2001 and 2010.
The intensely private couple Wednesday in 2010 after a whirlwind romance.
"He just meant 'I can't think about this today, ' having just done one", she said. It was not an ambition of mine. On the other hand the James Bond star had a daughter with ex wife Fiona Loudon in 1994.
Daniel Craig, meanwhile, is preparing for his fifth and final outing as James Bond in the untitled "Bond 25" movie, set for release in November 2019.More news: Fan Blade, Engine Cover Are Factors in Southwest Flight 1380 Engine Failure
This will be the couple's first child together.
She confessed that the steamy encounters were "softer" than anything she had filmed on-screen with a man.
She was also pictured on a solo outing at the Disobedience film photocall at the Four Seasons hotel in Beverly Hills on Wednesday, wearing a loose-fitting blazer.
She added: "I don't know if male actors ask this question, but I know women normally think, 'Is this sex scene really necessary?' In this case, it's essential".
When Sebastián Lelio's "Disobedience" premiered at the Toronto International Film Festival past year, everyone couldn't stop talking about the film's sex scene between stars Rachael Weisz and Rachel McAdams.
Kate became a mum at 38 and 42.
Of their relationship, she said: 'It's very personal, it's very private.