"It felt important to us to honour that relationship," said Holland. "I love them together, and I wanted to know that they were ending in a happy place."
"It felt like a great way to land these characters and like such a surprise coming off what their storyline had been," he added.
Molaro said the storyline allowed them to "jump over a lot of the pregnancy tropes and learn after the fact that Penny is two months pregnant".
"We did that [two-month] jump in time and she's still wrapping her head around it because Penny wasn't sure how she felt about it. I'm really happy that we were able to get in a direct nod to the pilot in Sheldon's final speech, too."
However the showrunners' explanations didn't wash with some viewers, who took to Twitter as soon as the finale aired to voice their concerns that the conclusion didn't mesh with Penny's previous character development.
"Just watched the #bigbangtheory #finale I'm a bit upset with the Penny's pregnant twist. She never wanted kids. Can't the storyline just be complete and fine without her having a giant change of heart? Sigh," wrote one.
"Lame choice to get Penny pregnant," criticised another. "We already had oops! pregnancies in the show (meh!) and now a childfree woman changes her mind because...? It's so cliché and dismissive of women."
"Disappointed the #BigBangTheory finale included a knocked-up and happy Penny after it was a big storyline that she didn't want kids. Things can end happily without someone getting pregnant, you know..." added a third.