One common theme could be the challenges they face as a couple during the pregnancy. Another might be how their relationship evolves with the new addition to their family on the way. There could also be themes related to the reactions of their friends and family in the story.
In Fourtris pregnant fanfiction, a frequent theme is the anticipation and excitement of the new life. It often explores how Tris and Four prepare for the baby, like setting up a nursery or choosing baby names. Also, there can be themes of overprotectiveness from Four towards Tris during her pregnancy. And sometimes, there are elements of conflict, like dealing with outside threats while Tris is pregnant.
I'm not sure specifically which Fourtris pregnant fanfictions are available. But you can try searching on fanfiction platforms like Archive of Our Own. There are usually a lot of works related to different themes for various fandoms.
One common theme is survival. Since 'The 100' is set in a harsh world, the pregnancy adds another layer of challenge. The characters have to ensure the survival of the mother and the unborn child in a world full of danger.
I'm not entirely sure as it could be a very specific fan - made story. It might be a fanfiction that combines elements from 'Divergent' and focuses on a relationship (Fourtris) and perhaps a new generation or a baby - related plot within that fictional universe.
Love and support are common themes. Usually, Bella's relationship with Edward or other important characters deepens as they support her through the pregnancy.
Another theme is the relationship changes. Her relationship with the baby's father might be explored, whether it's a new relationship or an existing one. There could also be changes in her friendships as she focuses more on her upcoming motherhood.
Family support is also a big theme. It shows how their friends and family react to the news, whether it's with joy, concern, or a mix of both. In some garmau pregnant fanfiction, the family members play an important role in helping the couple prepare for the baby.
One common theme could be the relationship changes. With the pregnancy, the characters' dynamics might shift in many ways.
One common theme could be the challenges of pregnancy. Since Undyne is a strong character, it might be interesting to see how she copes with the physical and emotional changes that come with pregnancy. Another theme could be the relationship between Undyne and her partner during this time, like how they support each other.
One common theme might be the anticipation and excitement within the family and the community. Since Neytiri is an important character in the Avatar universe, her pregnancy would likely have a big impact on those around her.
One common theme could be the exploration of the unexpected situation of a character like Chucky being involved in a pregnancy - related plot. It might also deal with themes of the supernatural and how it intersects with pregnancy.