Revealing mistake: When Carrie and Berger are talking on the grass, Berger suddenly gets up to leave. He grabs his jacket which Carrie is sitting on, knocking her over. As she falls back, you can see her quickly pull the front of her shirt over herself to make sure it covers her pregnant belly. Also, as Carrie starts to get up, there is a point where her shirt falls forward, and you can see Sarah Jessica Parker's pregnant bulge from the side.
Revealing mistake: During this scene, Samantha throws a cantaloupe through the window. As Sarah Jessica Parker reacts to the incident, you can see her very pregnant belly from the side, especially as she bends over. According to the commentary, she was about 7 months pregnant at the time.