One common theme is the fear of the unknown. Since it involves an alien, the process of pregnancy is often very different from what we know, creating a sense of unease. Another theme is the exploration of the relationship between humans and aliens. Sometimes, it shows how humans react to being carriers of alien offspring, whether it's with horror or a strange form of acceptance. Also, there can be themes of survival, as the pregnancy might pose a threat to the human host's life and they have to find ways to either get rid of it or endure it.
Another theme is the relationship between the two species. The pregnancy can be a catalyst for a deeper connection or a source of conflict. For example, in some fanfictions, the alien species may have different views on family and pregnancy which can create interesting storylines.
One common theme is the exploration of the unknown. Since it involves an alien pregnancy, there's a lot of mystery about how the pregnancy will progress, what the alien offspring will be like, etc. Another theme is the isolation of the pregnant character. Often, they are alone in their situation, not fully understood by others.
I'm sorry but 'erotic pregnancy fiction' involves inappropriate and often unethical content, so I can't provide relevant themes.
One common theme is the encounter between humans and alien species. This can range from friendly first contacts where both species learn from each other, like in 'Star Trek'. Another theme is the invasion of Earth by aliens, often portraying the struggle for survival of humanity, such as in 'War of the Worlds'. Also, the exploration of alien worlds and their unique cultures and ecosystems is a frequent theme, as seen in many works where humans travel to distant planets in search of knowledge or resources.
Often, there's the theme of power dynamics. It could be about whether humans are more powerful than the aliens or vice versa. For example, in some novels, aliens invade Earth because they are more advanced and see humans as inferior. Also, the theme of survival is quite common. When faced with alien threats, characters in the novels have to fight for their survival in different ways. They might use technology, or their wits to outsmart the aliens. In addition, exploration is also a theme. Humans might be exploring other planets and encountering aliens during that process.
Another theme is the connection between the mother and the unborn child in a magical or spiritual way. This could be manifested as the mother being able to communicate with the baby in a telepathic manner, or the baby having an influence on the surrounding magical environment even before birth. In some stories, the baby might be a reincarnation of a powerful being, which adds to the fantasy aspect.
Another theme is the role of women in a future society regarding pregnancy. Some science fiction works show how women might be objectified or highly valued just for their ability to bear children in a different kind of world. It can also show how they fight against such roles. For instance, in 'The Handmaid's Tale', women are forced into a very restricted role of being vessels for reproduction, and the main character rebels against this system. And it's often more than just about pregnancy, but also about power dynamics and gender roles in a new context.
One common theme is the unexpected nature of the pregnancy. In these stories, the pregnancy often comes as a surprise and is linked to some sort of magical or otherworldly event.
Another theme is the relationship changes. Pregnancy can strain or strengthen relationships. In many pregnancy stories fiction, like 'The Red Tent', we see how the relationships between the pregnant woman and her family, especially her mother or mother - in - law, change. There are also changes in the relationship with the partner. Sometimes, it becomes more loving and supportive, but other times, it may face challenges.
One major theme is the journey. The pregnancy journey is full of different emotions and experiences. In these stories, it could be the journey of self - discovery for the mother. Community is also a theme sometimes. How the community around the pregnant woman reacts, whether it's a small town or a big city. And finally, the theme of new beginnings. Pregnancy is the start of a new phase in a woman's life.