DK Ninpu Kurosaki-kun no Shussan

Jin Kurosaki is a high school boy who spends his days in irritation and apathy. That is, until he falls down a flight of stairs one day to save a pregnant lady named Mai and...ends up swapping bodies with her?! Suddenly becoming a pregnant lady is a lot to take in, but Mai's cheeriness and positivity help him face the situation. As feelings he's never felt before begin to sprout, he also starts to learn more about Mai and the secret she holds. (Source: Manga Plaza)