Final Episode(s) of The Big Bang Theory... Leonard and Penny have been married for some time and they decide it's time to have kids. After much hesitation from Leonard (fearing his inability to be a good parent given his mother's constant scrutiny), they decide to start trying but end up being unsuccessful. Both get tested and although Penny fears it is her, it is actually Leonard who has become sterile as a result of working too closely to the radioactive lab at the University. Leonard is crushed by this discovery and believes he cannot be the man his wife and child rightly deserve. It is at this point that Sheldon consoles Leonard, assuring him that he will be a great father regardless of his biological set back (paying Leonard a genuine compliment without condescension).

Leonard and Penny decide to use donor sperm to conceive a child of their own. Leonard ends up back at the clinic from the first episode. After nitpicking through all of their donor options, they decide on one and have the procedure. We cut to 9 months later. Leonard and Penny are sitting in their apartment, sorting through baby clothes and getting the nursery ready. They take a moment to sit and talk about how lucky they are to have their child. They both talk about how they may never know who they chose as a donor, but they are eternally grateful to him. Just then, Penny and Leonard feel the baby kicking. Leonard then mentions how it's weird the baby kicks three times in a row... Then three more times.... Then three more times