She gave birth to Cece in The Delivery.
Peggy Stewart played Pam's "meemaw" in the wedding episode.
The Convention! Season 3 Episode 2!
"Dunder Mifflin Infinity"
That occurs in the very first episode of The Office in Season 1.
Season 3, Episode 18: The Negotiation.
During Season 5, Pam goes to art school in New York. She returns to the Dunder Mifflin office in Episode 8.
Viewers found out that Pam was pregnant in the season five finale titled "Company Picnic".
Niagara: part 2 ! It was awesome
Season 3 Cocktails
In Season 2, Episode 6, in episode labeled "The Fight." Jim and Pam are playing around at Dwight's dojo, and Jim lifts Pam into the air. She gets very uncomfortable.
season 3 episode 13 half way through the episode
In season five, in the episode entitled Stress Relief.