According to Mayim Bialik, Amy wasn't conceived as a scientist yet in the previous episode, The Lunar Excitation (2010). During the gap between seasons 3 and 4, Bill Prady decided that Amy should be a neurobiologist, since Bialik has a PhD in neuroscience and could thus portray the character more accurately as the show's neuroscience consultant.
Vernee Watson, who plays the triage nurse, also plays the receptionist at the sperm clinic in the pilot. She also played a triage nurse in the season 1 episode The Peanut Reaction (2008), and she played a nurse in Chuck Lorre's other show Two and a Half Men (2003).
The term "Shamy", that represents a combination of the name Sheldon and Amy, was first introduced by Howard.
In the Season 2 episode The Barbarian Sublimation (2008), Penny states that she hasn't had sex in 6 months. Therefore, Sheldon's estimated numbers regarding Penny's sexual partners would have to be lower.
Sheldon has his first date, since going square-dancing with his twin sister at a Teens for Jesus Fourth of July did not count as one.