As previously reported, O'Hara, who received a Tony nomination for her portrayal of Ensign Nellie Forbush, will depart the production March 7 in anticipation of the birth of her first child.
O'Hara, it has also been announced, will return to the Tony-winning revival of South Pacific on Oct. 6.
Laura Osnes made her Broadway debut as Sandy in the 2007 revival of Grease following a talent search on the reality-television competition "Grease: You're The One That I Want." She was also recently seen in the Kennedy Center's Broadway: Three Generations concerts.
Tony winner Bartlett Sher directed the Tony-winning South Pacific revival.