One common theme is secrecy. Since Merlin's situation is so unique and perhaps not fully understood in the context of Camelot, he often has to keep his pregnancy a secret, which creates a lot of tension in the stories.
One idea could be that it's a magical pregnancy. Maybe Merlin was accidentally affected by a spell meant for someone else, and now he's pregnant with Gwen's baby in a very strange and magical way. This could lead to a lot of confusion and drama in Camelot as they try to figure out how to handle this unprecedented situation.
One common theme is the challenges she faces. Since Merlin is usually depicted as a powerful figure in the Merlin universe, being pregnant might limit her abilities in some ways, and this can create a lot of internal and external conflicts. For example, she might have to hide her pregnancy from certain characters who could pose a threat.
One place to look for such fanfiction could be Archive of Our Own (AO3). There are often various Merlin - related fanfics there, and by using the search function and typing in relevant keywords like 'fem merlin pregnant', you might find some interesting stories. However, I can't specifically recommend a single one as there are so many different works with different plotlines and writing styles.
Their relationship would likely become more complex. They would have to rely on each other more, as they are now bound by the unborn child. There would be a new level of trust and vulnerability between them.
One popular 'pregnant Merlin fanfiction' might be 'A New Beginning' which explores Merlin's journey while pregnant in a very heartwarming way. It delves into how he copes with the changes and the reactions of those around him in Camelot.
You could also develop the plot by focusing on the physical and emotional changes Merlin goes through during the pregnancy. He might struggle with the hormonal changes, just like any pregnant person would. Emotionally, he could become more protective of Gwen and the unborn baby. Meanwhile, they might have to deal with threats from outside forces who somehow find out about the pregnancy and want to use it for their own gain. This could add a lot of action and suspense to the fanfiction.
If Merlin died in the fanfiction, it could trigger a series of tragic events. The balance of power could tip, and the villains might seize the opportunity to attack. It could also bring out hidden strengths in the remaining characters as they try to cope with the loss.
There might be. Fanfic communities are quite creative. However, the availability may vary. Some platforms may have a good number of such fanfics while others might have fewer. You could also check out some Merlin - related forums where fans might share or recommend such stories.