The 37-year-old actress - who is engaged to marry Will Kopelman - is still planning on her wedding despite being pregnant, and wants to use her home in Montecito, California, as the venue for the ceremony.
A source told Us Weekly magazine: "She is so thrilled to be expecting.
She is really focused on the wedding right now. She will be even more excited about the baby after that.
"The expectant mother is planning to wear Chanel for the big day. Drew - who has been wed twice before to bar owner Jeremy Thomas for just two months and comedian Tom Green -is believed to be expecting a baby girl, and has previously revealed her hope she would have a daughter to expand her family.
She said: "I feel I'm sort of surrounded by children and I do feel I'm going to have a child at some point. Maybe a little girl. I feel it, but I don't know if it's going to happen. We'll just have to wait and see."