There are some fanfictions that might explore such a scenario. However, it depends on different authors' creativity and the specific plotlines they develop. Some fanfic writers might be interested in exploring the relationship between Mara Jade and Luke Skywalker in such a context, but it's not a mainstream or canon storyline in the official Star Wars universe.
One possible plot could be them going into hiding to protect the unborn child from their enemies. Since they are both important figures in the Star Wars universe, there would be many who might want to harm the child for various reasons, like power or revenge.
Sith cults could also be antagonists. They might sense the power of the unborn child in the Force and want to turn it to the dark side. They could launch attacks on Luke and Mara to either kidnap Mara or influence the unborn child through dark side magic or the Force.
One great fanfiction could be 'The Bond of Skywalker and Jade'. It delves deep into their relationship, exploring how their Force sensitivities interact. Another is 'Luke and Mara: A New Adventure' which takes them on a journey across the galaxy to face a new threat. There's also 'Mara Jade's Choice' that focuses on Mara's internal struggles regarding her feelings for Luke.
Some popular authors are 'JediWriter123'. Their stories often have a great balance between action and romance for Luke and Mara. Another one is 'StarWarsFanatic456' who is known for really delving into the characters' emotions. And 'GalaxyTalesAuthor' also writes some great fanfiction about them.
Character growth is another major element. Mara Jade might start off as a bit of a mystery, and through her interactions with Luke, she evolves. Luke, too, may change as he gets closer to Mara, learning new things about himself and the Force, as seen in some fan fictions where he discovers new aspects of the Force through her influence.
One possible storyline could be that they face challenges from the dark side while Mara is pregnant. Maybe some remnants of the Empire try to target them because they see the unborn child as a potential threat or a powerful force for the light side. They would then have to go into hiding and rely on their friends and allies to keep them safe.
One interesting plotline could be their first meeting in a different context. Maybe instead of how it happened in the official lore, they meet during a smuggler's run. Luke is on a mission to retrieve an important Jedi artifact and Mara Jade, working undercover for the Empire at the time, is also after it. Their encounter could lead to a series of adventures as they battle pirates and other foes while trying to outwit each other.
One great Mara Jade - Luke Skywalker fan fiction is 'Heir to the Empire' series. It really delves into their relationship in an interesting way, with great character development and a captivating plot that keeps you hooked. The way it weaves their individual stories together is quite remarkable.
In certain fanfictions, their shared experiences of loss bring them closer. Both have lost a lot in their lives. Luke lost his family and mentors, and Mara Jade lost her connection to the Empire. This common ground makes them more empathetic towards each other. They support each other in their personal growth, with Luke helping Mara Jade explore the light side of the Force and Mara Jade teaching Luke some practical survival skills that she learned during her time in the Empire.