“We had talked a lot earlier this season about honoring the pilot, how ‘our babies will be smart and beautiful.’ It was a special moment to us. To bring that back around in the finale felt important, he said.
“It also felt a little bit like people were expecting it, so to write against it all season felt like a way to make that moment play as more of a surprise,” he added.
And with that, the decision was made to change Penny’s stance on having kids and make her an expecting mother just before the end. It wasn’t a decision that Kaley Cuoco was entirely on board with, however.
I actually wished that they did not [make Penny pregnant], because I loved that message of Penny not wanting kids so much,” Cuoco was quoted saying in a Big Bang tell-all book by Jessica Radloff, per Screen Rant.