The newly married superstar is reportedly pregnant with her third child.
Us Weekly magazine is reporting in its new issue that Witherspoon, who will celebrate her 36th birthday Thursday, is expecting a baby with her second husband, Jim Toth.
"Reese is right around 12 weeks," a source told Us Weekly.
The baby would be the first child for the Oscar-winning actress and Toth, a well-known Creative Artists Agency agent whom she wed last March at her $7 million ranch in Ojai, Calif.
Witherspoon is already mom to 12-year-old daughter Ava and 8-year-old son Deacon Reese, her children with first husband Ryan Phillippe. The two actors divorced in 2006 after seven years of marriage. The pair met at the actresses' 21st birthday party and starred together in 1999's "Cruel Intentions."
Witherspoon has been traveling the world in recent weeks to promote her latest movie, "This Means War." She is set to appear next alongside Cameron Diaz and fellow Hollywood mom Gwyneth Paltrow in the film "One Hit Wonders," directed by "Glee" creator Ryan Murphy.
While Us cites multiple sources in announcing Witherspoon's pregnancy, the only confirmation the public might get are sightings of a baby bump on the petite star. At least one source told the magazine Witherspoon and Toth are "not planning" to announce the pregnancy.
Witherspoon recently opened up to Britain's TV show " Daybreak" about preparing herself for the day when her kids become teens and gain their independence.
"There's a little sadness as they're growing up and walking away from you, but it kind of changes the whole dynamic," she said. "We have really funny dinner conversations now, and they know more about certain topics than I ever, ever knew."
Witherspoon, who according to Us sources' timeline would have been pregnant during the Feb. 29 interview, did say, "I like babies, too. I hug all my girlfriends' babies. They're all so stinking cute."
In an interview last year with Marie Claire, Witherspoon opened up about the emotional weight that has been lifted from her since marrying Toth.
"I feel so much relief," she said. "I don't think I recognized how anxious I was about being a single parent. It was really, really stressful. It's not easy on anybody."