I'm not sure if there is specifically a Takaba Akihito pregnant fanfic. Fanfics can cover a wide variety of themes and scenarios, but it might be a rather niche or less common one. You could try searching on fanfic platforms like Archive of Our Own or Fanfiction.net, but there's no guarantee you'll find one.
A plotline might involve Takaba Akihito's partner's reaction to the pregnancy. It could be a story of them coming together to support each other through the journey, or there could be some initial conflict if the partner wasn't ready for a child. Also, Takaba Akihito could be in a situation where he has to balance his career or personal goals with the pregnancy.