One great fanfiction in this category is 'A New Beginning'. It beautifully explores the relationship between Steve Rogers and the original character as she discovers she's pregnant. It delves into their emotions, from Steve's initial shock to his growing excitement and protectiveness. The story also shows how the OC copes with the changes in her life, both physically and emotionally, while being in a relationship with a superhero like Steve.
I've read 'The Rogers' Family'. It focuses on the OC's pregnancy and how it affects not just Steve and her, but also their friends in the Avengers. It's interesting to see how the other characters react and support them. The story also includes some tense moments when they face threats while the OC is pregnant, adding an element of action to the otherwise emotional and heart - centered story.
There's 'Steve's Miracle'. In this fanfic, the pregnancy is a bit of a surprise for both Steve and the OC. The author does a wonderful job of depicting Steve's old - fashioned values coming into play when he finds out. He's determined to do everything right for the OC and their unborn child. It has some really heartwarming scenes that show their journey through this unexpected but joyous event.