One common theme could be the challenges the character faces during pregnancy. This might include dealing with her own fears and insecurities, as well as how others around her react to the news.
I'm sorry, but I'm not aware of specific 'fem hiccup pregnant fanfic' stories. You can try searching on fanfic platforms like Archive of Our Own. They have a large collection of various fanfictions, and you might be able to find what you're looking for there.
I'm not sure specifically if there is a 'hiccup haddock pregnant' fanfic. There are so many fanfics out there in the vast world of fandom, and it might be difficult to determine the existence of one with such a specific theme without doing a thorough search on fanfic platforms.
I'm not sure if there is an official such fanfic. Fanfics can cover a wide range of themes and scenarios, but this one might be a bit controversial or not in line with the original story's tone in some views. However, the fanfic community is so vast that there could potentially be something like it out there.
One possible plot could be that in a magical realm where the bond between Toothless and Hiccup is even more profound, an ancient spell or some kind of strange phenomenon causes Hiccup to be able to conceive. Toothless, being extremely protective, would then go to great lengths to keep Hiccup safe during the pregnancy. He might search for special herbs or a safe place for her to give birth. And along the way, they face challenges from those who don't understand this strange occurrence.
Toothless would likely develop his communication skills further to better understand Hiccup's needs during the pregnancy. He might start to make more complex gestures or sounds. Hiccup would experience a great deal of personal growth. She would have to face the judgment of the village and learn to stand up for herself and her unborn child. The other dragons in the story could also develop in their relationships with Toothless and Hiccup. For example, they might initially be confused but then show support in their own dragon - like ways.
A common theme is the exploration of an unusual bond. Since it's a cross - species relationship, there's often a focus on how they overcome the differences. Another theme is mutual understanding. Hiccup and fem Toothless have to understand each other's needs and wants. For example, in many fanfics, Hiccup learns to communicate with fem Toothless in new ways.
One key element is the unique dynamic. Since Hiccup is female, it often changes the nature of the relationship with Toothless. There's usually more of an emotional connection that's explored in a different way than in the original male Hiccup story. Another element is the adventures they go on together. These can be new and exciting, as the fem Hiccup may approach situations differently.
Another place to look might be Fanfiction.net. It has been around for a long time and has a wide variety of fanfics. However, the search functionality might not be as advanced as some other platforms. So, you'll need to be patient and search through different categories related to the 'hiccup haddock' story to see if you can find what you're looking for.
One popular 'fem Toothless x Hiccup' fanfic is 'Flight of the Heart'. It beautifully explores their relationship in a new light, with detailed descriptions of their interactions and how their bond grows. Another one is 'A New Bond', which focuses on how Hiccup discovers the fem Toothless and the challenges they face together in a world that's not quite ready for their unique connection.