It can have a huge impact. First, it changes Hermione's character arc. She goes from being a student focused on her studies to someone about to become a mother, which is a big shift. Second, it can bring in new storylines related to parenting in the wizarding world. And it can also affect the relationships of other characters. For example, her friends might feel more protective or might have mixed feelings about her situation.
The pregnancy in the fanfic universe could lead to new alliances and rivalries. Maybe some characters support Hermione wholeheartedly, while others see her as a liability or a threat. It also might introduce new magical elements related to pregnancy and childbirth in the wizarding world. For instance, there could be special spells or potions to ensure a healthy pregnancy, and Hermione might be at the center of exploring these things.