Drew announced that she is expecting a child last week, prompting speculation about storylines for her character April.
Last season, it emerged that April is a virgin.
Recent rumors had suggested that April could have sex for the first time in a future episode, but Rhimes has now confirmed that she is not planning to make April pregnant.
"April Kepner is a virgin and we'd have to work really fast to get April unvirginised, pregnant, and having a baby by January [when Drew's baby is due]," Rhimes told TV Guide.
"That feels a little insane, so I don't think we want to speed that story up. We're quite good at hiding things like that, so we'll do what we always do."
Last season, cast member Jessica Capshaw missed a couple of episodes while she was expecting her second child, but her pregnancy was not written into the show.
Grey's Anatomy will return with a two-hour premiere on September 22 on ABC.