Charmed (1998): Season 5, Episode 4

5 - 4: Siren Song

Cole and Phoebe both fall under the spell of the Siren, who lures husbands to her and entrances their wives to follow with the intent to kill, leaving Piper and Paige to figure out how to save Phoebe. Piper, upset with Leo because he does not understand the challenges of being pregnant, and Leo, frustrated that Piper does not realize the demands of being a Whitelighter, have their personas switched magically by their unborn child.