The couple have been married for four years, but have reportedly resorted to fertility drugs in order to conceive. Says a source, "Ashton has been uneasy that things haven't happened fast enough. He's constantly calling the doctor to find out if there is something else they can do to get pregnant. It has to be exhausting. He's ready to be a dad."
If they do get pregnant, Demi will join a growing group of Hollywood stars who have conceived in their late 40s, including Susan Sarandon, Holly Hunter, and - most recently - Kelly Preston.