Perhaps in this fanfiction, the pregnancy is not a normal one. Due to the Doctor's Time Lord biology, there could be some strange and unexpected things happening to Rose during her pregnancy. For example, the baby might have some unique powers or abilities even before it's born. The Doctor would have to use all his scientific knowledge and his TARDIS to ensure the well - being of Rose and the unborn child.
In the fanfiction, Rose's pregnancy could be a catalyst for the Doctor to finally settle down in one place for a while. Maybe they find a peaceful planet where they can build a home and prepare for the arrival of the baby. Their friends from their adventures might come to visit and offer their support. It could also lead to some interesting cultural clashes as they combine their different upbringings and knowledge to raise the child.
A great idea for this fanfiction could be that Rose starts having dreams about their future child. These dreams could give them clues about the baby's purpose or the challenges they will face. The Doctor would be very interested in these dreams and try to analyze them scientifically.
Another idea is that they are in a time - locked situation where they are cut off from the TARDIS. They must rely on their wits and the help of some new friends they make in that situation to survive during the pregnancy. It could also be a chance for Rose to learn more about the Doctor's past as they wait for help.
The Doctor would likely be both excited and terrified. He'd be extremely protective. He might start modifying the TARDIS to be a safer place for Rose and the baby, adding things like special shields or a nursery area.
Adventure is another theme. Since they travel through time and space together, many fanfics have them going on all sorts of exciting adventures, whether it's saving a planet or exploring a new era. It adds to the overall charm of their relationship as they face these challenges together.
One idea could be that they discover the pregnancy in the middle of an adventure. Maybe they're on a planet with some strange energy that affects the Doctor's biology in an unexpected way, leading to the pregnancy. They then have to deal with the challenges of protecting the unborn child while also facing the usual threats in the universe.
Another interesting one is 'Parallel Worlds'. In this fanfiction, it explores different parallel universes where the Tenth Doctor and Rose's relationship takes on various forms. It's full of creative ideas and really makes you think about the possibilities of their relationship.
One popular theme is the adventure aspect. Fans often write about the baby growing up in a world full of time - traveling and alien encounters, just like the Doctor and Rose had. Another theme is family. It could be about how the Doctor, Rose, and their baby form a unique family unit, dealing with the challenges of being part of different species. Also, the theme of protecting the baby from various threats, both from within their own universe and from other dimensions, is quite common in these fanfictions.
A common plot in such fanfiction is a kiss that seals a promise. For example, the Tenth Doctor might promise Rose that he'll always be there for her, and the kiss is a physical manifestation of that promise. It can also be a kiss that occurs during a time-travel adventure. Maybe they are in a beautiful historical setting, and the moment just calls for a romantic kiss.
I'm not sure if there is a specific fanfiction exactly with those elements. Fanfiction can cover a wide range of scenarios, but this seems rather inappropriate and not in line with the general respectful portrayal of the Titanic story. The Titanic story is often remembered for its tragic and romantic aspects in a more refined way.
The fanfiction might be a heartwarming tale of their journey together during Rose's pregnancy. Or it could be a thrilling action-packed story with them facing off against powerful foes.