She may be using Muggle methods as well. In the wizarding world, Muggle things are sometimes overlooked. She could be wearing loose - fitting clothes that hide her growing belly. Also, she could be using Muggle - style makeup to disguise any changes in her face, like puffiness or a different complexion. Hermione is well - versed in Muggle culture, so she would know how to use these methods effectively to keep her pregnancy a secret from Draco.
She could be using magic. For example, she might use a concealment charm on herself to hide any physical signs of pregnancy. Hermione is very skilled in magic, so she could easily cast spells that make her look the same as before. She might also avoid situations where she would be in close contact with Draco. By staying away from him as much as possible, she reduces the chances of him noticing any changes in her.
Naruto could use clothing to her advantage. Wearing baggy and androgynous ninja outfits would help to conceal her feminine body shape. For example, the standard orange jumpsuit she often wears doesn't really give away her gender easily.
One possible reason could be fear. Maybe Hermione is afraid of how Draco will react. Given their history in the wizarding world, with their houses being rivals at Hogwarts and different beliefs, she might think he'll reject her or the baby. Another reason could be to protect the baby. There could be some threats or dangerous situations in the wizarding world that she believes Draco's knowledge of the pregnancy would put the baby at risk. For example, there could be dark forces that target the children of powerful witches and wizards, and she wants to keep the baby's existence a secret to safeguard it.
She probably uses magic. For example, she could use a spell to mute any sound coming from her music player when someone gets too close. Or she might have a charmed diary where she writes about her love for the singer and it can only be opened by her magic signature, so no one else can find out.
Often, the plot develops with Hermione constantly being on edge, trying to avoid Snape as much as possible. She might start making excuses to skip classes or meetings where she knows Snape will be present. For example, she could claim to be working on an important research project alone in the library. Meanwhile, she may confide in her close friends like Harry and Ron, but make them swear to keep it a secret.
Well, perhaps Snape uses his position as a teacher to step in. He could have been observing the situation secretly and when Draco was about to do something harmful to Hermione, Snape intervened with a firm command or some magic spell to stop Draco in his tracks.
She could use a magic - suppressing charm. This charm would make it so that her natural magical aura is hidden from other wizards and even from magical detection devices. For example, if a wizard were to pass by her with a magical detection spell active, they wouldn't sense her magic. Another way is by only using very basic and small - scale magic when absolutely necessary. Like if she needs to light a candle in a power outage, she might use a very tiny and discreet fire - making spell that looks almost like a normal match being lit.
Hermione could be hiding her pregnancy from Snape because she's not sure of his feelings towards her. There may be an ambiguous relationship between them. She might be in love with him, but not sure if he feels the same. And she doesn't want to burden him or make things awkward between them. Or perhaps she suspects that Snape might be involved in something dangerous, and she doesn't want her unborn child to be dragged into it.
Well, in some versions, Ron might use his quick wit and knowledge of Hogwarts' secret passages to outmaneuver Draco. He could lead Hermione to safety through a passage that Draco doesn't know about.
One possibility is a spell gone wrong. Maybe they were both involved in some sort of experimental magic in the library or an abandoned classroom, and the spell had unforeseen consequences on their physical states.
Well, in some fanfictions, Lucius might use his charm and power. He could be depicted as very persuasive and use his status in the wizarding world to make Hermione see him in a different light. Maybe he offers her opportunities for knowledge or power that she doesn't get with Draco.