The pop diva will star alongside Cameron Diaz in the romantic-comedy adaptation of the bestselling pregnancy guide
"What to Expect When You're Expecting" is based on Heidi Murkoff's pregnancy manual, a New York Times bestseller for more than 500 weeks. Heather Hach wrote the screenplay adaptation after selling it as a pitch in a fierce bidding war. Shauna Cross rewrote.
Lionsgate plans to release the movie on Mothers Day weekend 2012.
The movie tells four related stories. Lopez's arc focuses on Holly, who has difficulty conceiving a child with her husband and wants to adopt a baby from abroad.
Lopez's last movie was "The Back-Up Plan," released in April 2010. Since then, she revitalized her career by becoming a judge on "American Idol."
"What to Expect When You're Expecting" begins filming this summer.