Well, one possibility is that it could add a whole new layer of complexity to the story. Peeta might be overjoyed and become even more protective of Katniss. Their relationship could deepen as they face the challenges of not only the Capitol but also impending parenthood. It could also change how the other tributes view them, perhaps some might see them as more vulnerable, while others might respect them even more for having to deal with this on top of the Games.
One possible scenario in the fanfiction could be that Katniss and Peeta's baby becomes a symbol of hope in the districts. The baby might grow up with unique skills inherited from its parents. For example, having Katniss's archery skills in a more developed way in the future. It could also be that the baby's existence is a threat to the Capitol, so they have to keep it hidden and protected at all costs.
The pregnancy in the fanfiction could also impact the relationships between the characters. Gale might have a different reaction, perhaps feeling a bit jealous or more determined to protect Katniss and the baby from afar. And Haymitch would probably have to come up with new strategies to keep Katniss and Peeta alive, considering the added factor of the pregnancy. It could also lead to new alliances in the arena, as some tributes might see the value in protecting a pregnant Katniss for the sake of the rebellion.
The plot could revolve around the baby being born in a secret location. Katniss and Peeta would be extremely cautious about protecting the baby's identity. The Capitol might get wind of the baby's existence and send out troops to search for it. This would lead to a series of chase scenes and close calls as Katniss and Peeta use their survival skills to keep the baby safe.
Finding a 'lemon' fanfic specifically for Katniss and Peeta in 'Catching Fire' can be a challenge. 'Lemon' content often goes against the terms of use of many fanfic platforms. However, if there are some underground or less - regulated fanfic communities, there could be something. But it's important to note that such content may not be in line with the original spirit of the 'Hunger Games' series and can also be of poor quality or inappropriate in nature.
Their married life might be a mix of peace and chaos. Since they got married, they could be a symbol of hope for the districts. Peeta, being the kind - hearted one, would probably do everything to make Katniss happy. He might bake special treats for her. Katniss, on the other hand, would protect their home. They'd probably have to keep a low profile at times to avoid trouble from the Capitol. And at night, they'd share stories of their past, strengthening their bond.
Once they are married in the fanfiction, their relationship undergoes a significant transformation. They begin to understand each other on a whole new level. Katniss realizes how much Peeta truly means to her and starts to show her affection more openly. Peeta, for his part, feels more secure in their relationship. They become a team, working towards the betterment of their district and the safety of their loved ones. Their marriage gives them a sense of purpose and a stronger connection to fight against the oppression in Panem.
Well, if Katniss was pregnant in fanfiction, it could bring a lot of emotional turmoil and difficult decisions. It might also affect her relationships with other characters and how they respond to her situation.