You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfiction for various fandoms, including ones about Sarah and Jareth's love.
Some smaller, more niche fanfiction communities dedicated to the Labyrinth might also have great Sarah and Jareth love fanfiction. You can find these by searching for Labyrinth - related forums or groups on social media and then exploring the fanfiction sections there.
You can try fanfiction platforms like Archive of Our Own (AO3). It has a large collection of various fanfictions, and you're likely to find some great 'Jareth loves Sarah' ones there.
You could try specialized Labyrinth fanfiction forums. These are often filled with die - hard fans who might have written or know where to find 'Jareth x Sarah pregnant' fanfiction. Additionally, some Discord servers dedicated to Labyrinth fandom could also be a good source. You can ask around in these communities and see if anyone can point you in the right direction.
The relationship might become more intense. With the pregnancy, they have to rely on each other more. Jareth may show his softer side as he takes care of Sarah, and Sarah might start to see him in a new light, beyond the intimidating Goblin King.
One popular one might be 'The Labyrinth of Love' which delves deep into their relationship. It shows how Sarah overcomes her initial fears of Jareth and they start to understand each other on a deeper level.
There is a fanfiction called 'Love Beyond the Labyrinth' where Sarah, after getting lost again in the labyrinth, discovers a new side of Jareth and they start to explore their romantic feelings. It has really detailed descriptions of their emotions and the magical setting.
Love in this fanfiction could be shown as a force that gives them the strength to face the unknown. The pregnancy is full of uncertainties, like what the baby will be like, how they will raise it between two worlds. But their love for each other and the baby gives them the courage to face all these questions. They support each other emotionally, and their love becomes the foundation for building a family, despite all the odds against them.
A common theme is the exploration of their unspoken connection. Since in the original there's a certain tension between them, fanfictions often expand on that, like in 'The Unspoken Bond' where it's all about their unacknowledged feelings for each other.
One great Jareth and Sarah fanfiction is 'The Labyrinth's Echo'. It beautifully explores their relationship post - the events of the Labyrinth. The author really captures the essence of Jareth's allure and Sarah's growth.
The story might end with Sarah actually falling in love with Jareth. She decides to stay in his world and they rule the Goblin Kingdom together, bringing a new era of peace and harmony between the human world and the Goblin realm. This would be a very different ending from the more common 'escape and return home' trope.
One common theme is the power dynamic between them. Since Jareth is a powerful Goblin King and Sarah is a mortal girl, exploring how their relationship develops in terms of power is popular.