When on charmed does piper get pregnant with Wyatt?

Piper Halliwell becomes pregnant with Wyatt in Season 4 of "Charmed." Specifically, her pregnancy is revealed in the episode titled "Something Wicca This Way Comes," which is the 18th episode of that season. Wyatt is born in the Season 5 finale, "Forever Charmed." Piper's pregnancy is a significant plot point that adds to the series' themes of family and legacy.