Trivia: The actress who plays Debbie is Leslie Mann, and she is the real-life wife of writer/director Judd Apatow. And the two girls who play Debbie's daughters are their daughters in real life. This was done on Apatow's part to make the on-screen family seem more like a real family.
Trivia: Similar to The 40 Year Old Virgin, much of the dialogue in this movie was improvised.
Trivia: Ben's roommates (Jay, Johah, Jason and Martin) are all friends of director Judd Apatow and star Seth Rogan. And in fact, they are even using their real first names. Only Rogan (who portrays Ben Stone) used a fake name, and was the subject of many flub-ups, as the gang would frequently accidentally call him by his real name.
Trivia: Many of the events in this film (including Ben being kicked out of the car, the gynecologist not showing up to the birth, and other major details) are based on things that happened to writer/director Judd Apatow when he and his wife (actress Leslie Mann) had their two daughters.
Trivia: Director Judd Apatow originally wanted to shoot footage of a real woman giving birth for the final scene in the hospital, and he even found a willing mother-to-be. However, a union dispute botched the idea, when Apatow learned that he could only shoot babies that were registered Union-members (presumably registered by their parents). This is all confirmed in the DVD commentary.
Trivia: David Krumholtz was supposed to be in the film as one of Seth's friends, but he dropped out when he got offered the lead in a Woody Allen film. Unfortunately, that film ended up falling apart during pre-production and was never made.
Trivia: As the phrase "Knocked Up" is pretty much exclusively an English phrase, the title was changed in most other countries. Notable, in many countries it was released under the title "A Little Bit Pregnant" or "Slightly Pregnant."
Trivia: In the opening scene, you can see that Jay is incredibly nervous while on the roller-coaster - this is actually a real reaction, as actor Jay Baruchel is deathly afraid of roller-coasters in real life.
Trivia: The film was originally conceived as a sequel/spin-off to "The 40 Year Old Virgin," but all connections were dropped early on in the production.
Trivia: Like "The 40 Year Old Virgin" before it, "Knocked Up" is one of the somewhat rare films to shoot over 1 million feet of film due to all the improvising and extra takes.
