 On the day she shot the scene where she goes to the Paris Cinema to  see "Joy for Two" and it later rains very heavily,  Sarah Jessica Parker (qv) wasnt feeling well, so she sent her  assistant to fetch her a home pregnancy test. She learned she was in  fact pregnant just before shooting the scene; scripted as a rather  giddy, happy scene (it is in the episode, "Anchors Away!"), this  obviously helps explains why she is extra