Society in general could be an antagonist. If Maura and Frankie are in a situation where their pregnancy is not fully accepted, like in a very conservative community. The pressure from society to conform to certain standards and not have a baby at their stage in life can be a major obstacle for them.
Maybe Maura's over - controlling mother could be an antagonist. She might try to force Maura into making decisions she doesn't want, like giving the baby up for adoption against Maura's will.
One possible plot could be that Maura and Frankie are in a relationship and the unexpected pregnancy throws their lives into chaos. They might have to deal with family reactions, like Frankie's family being overjoyed while Maura's is more hesitant. And they start to plan for their future together, including finding a new place to live.
One great fanfic could be one where Frankie and Maura's journey through pregnancy is filled with humor and a lot of heartwarming moments. For example, they might deal with crazy pregnancy cravings together and support each other through the mood swings. It could also show how their friends and family react to the news, adding more layers to the story.
Another theme is the relationship changes. The pregnancy can bring a new level of closeness or some challenges to their relationship. They might have different ideas about parenting styles, which could lead to some conflicts but also opportunities for growth and understanding.
Friendship could be a common theme. Maybe they go on adventures together, support each other through tough times, and have a deep bond that is explored in the fanfiction.
One antagonist could be an old enemy of Levi's who resurfaces during Petra's pregnancy. This enemy wants to take revenge on Levi by targeting what he holds dear, which is now Petra and their unborn baby. They might set up traps or create dangerous situations for the couple. Additionally, there could be some traditionalists in their military organization who don't approve of soldiers having a family and try to make their lives miserable during the pregnancy.
Frieza or his remnants could be antagonists. They might see the unborn child as a potential threat in the future, especially if it has strong Saiyan powers. So they could plan to attack Bulma to prevent the birth.
The gods could potentially be antagonists. If the pregnancy goes against some divine law or prophecy, they might try to interfere. For instance, Zeus could see it as a threat to the order of things and send his minions to cause trouble for Percy and Bianca.
The Capitol could still be the main antagonists. They might see Katniss's pregnancy as a threat, either because they fear the child could grow up to be a symbol of resistance like Katniss or just because they want to maintain control over her. They could try to harm her or the baby in some way.
The other vampires in Mystic Falls who are against the idea of a hybrid - vampire baby could be antagonists. They might see it as a threat to their way of life.
Other tributes or survivors who are jealous or resentful could also be antagonists. They might not like the idea of Katniss and Finnick having a family when they have lost so much themselves. This could lead to conflict and attempts to harm them or the baby.