It could be some of the traditional enemies they face. For example, the Foot Clan might see this as an opportunity to target them, thinking that a pregnant April and a distracted Raph would be easier to attack.
Another option could be some sort of government agency or anti - mutant group. They might see the pregnancy as a threat, fearing that the offspring could be a powerful mutant. So they try to interfere with Raph and April's situation, perhaps by trying to capture them or separate them.
Well, it could start with Raph and April having a deep emotional connection that leads to an unexpected pregnancy. Maybe they initially struggle with how to handle it, like dealing with the reactions of their friends and family.
It could be some of the nobles in the kingdom who are not happy with the idea of Rapunzel having a baby so soon. They might fear that the baby will disrupt the line of succession or cause political unrest. So they try to undermine Rapunzel and Eugene during her pregnancy, creating all sorts of problems for them.
In TMNT fanfiction, Raph getting pregnant could be part of a very creative and out - of - the - box plot device. It might be due to some sort of magical or alien influence in the fictional universe created by the fanfic writer. For example, an alien race with unique reproductive abilities could have affected Raph in a way that defies the normal biological rules of the TMNT world.
One potential antagonist could be those within the village who oppose Naruto's relationships. They might see his harem as a threat to the traditional values of the village and try to cause trouble for Naruto and his partners.
Elena could be an antagonist. Since she has a history with Christian, she might try to interfere with Anastasia's pregnancy, perhaps out of jealousy or a desire to maintain some control over Christian.
Another possible antagonist could be Zelena. Jealous of Belle's happiness and the new life she's bringing into the world, Zelena could try to cause trouble. She might use her magic to create false scares or difficulties during the pregnancy, like making Belle believe there are problems with the baby when there really aren't.
The main antagonists could be the same organizations they have always fought against. For example, Umbrella Corporation or any other bio - terrorist groups. These groups might see Ada's pregnancy as a weakness and try to use it against them. They could target Ada to get to Leon or try to harm the unborn child to stop Leon from interfering with their evil plans.
It could be Gabriella's over - protective father. He might think that Troy isn't ready to be a father and tries to convince Gabriella to break up with him. He believes that their pregnancy will ruin Gabriella's future and he's very strict about it, causing a lot of tension between the couple and him.
It could be some rogue ninjas who see Temari's pregnancy as a vulnerability and try to target her or Shikamaru. They might think that a pregnant Temari would be an easy target and that Shikamaru would be distracted, so they could try to carry out some evil plan against them.
One possible antagonist could be Blair. If she still has feelings for Nate, she might see Serena's pregnancy as a threat to her relationship with Nate, whether it's a real relationship or just her own feelings. So she could try to create problems between Nate and Serena during the pregnancy.