Well, a simple idea could be that the pregnancy is a secret at first. Only a few close allies know. Jon and Daenerys have to be very careful to keep it that way. They might have some close calls where the secret almost gets out, adding a lot of tension to the story.
Another aspect could be the magical implications of the pregnancy. Given the world of Game of Thrones has magic, perhaps the unborn child has some sort of special power. This could attract both good and bad forces, leading to various adventures and battles as Jon and Daenerys try to protect their child and themselves. This would make for a very exciting fanfic with lots of action and mystery.
The best chapter pointer here is Chapter 232, "He's a Pure Man! Purebred!". It opens with But soon, she suppressed this strange feeling and slowly began to speak,... and closes on The moment he saw the information come through, Jiang Li fell silent..
Look to Chapter 229 for the clearest answer. It begins with Huo Ziyang's face had already turned deathly pale., keeps building through Huo Xuan, how did she come to know about this?!, and lands on Isn't it enough to teach a child a lesson when he makes a mistake?.
Chapter 282 is the strongest chapter-level answer because it starts from The other villagers quickly heard the commotion and hurried over. and follows through on Why isn't there a live broadcast reporting on their itinerary?] [Could....
Chapter 236 is the strongest chapter-level answer because it starts from The short-haired youth beside them chimed in, "That's right, senior, we... and follows through on Everyone, try not to get too anxious." The crowd nodded, seemingly....
Look to Chapter 220 for the clearest answer. It begins with I know everyone has many questions, and I'm here to answer them one by..., keeps building through Actually, from the very beginning of the seed selection phase, we designed..., and lands on However, Su Yinwan and Shang Shaojing weren't.
Look to Chapter 264 for the clearest answer. It begins with Jiang Li first reassured her mother, then opened the chat box with Shen..., keeps building through She had just sent a message when Shen Lan's video call came through., and lands on [Do your faces hurt, you rumormongers?.
If you want the clearest chapter reference, go to Chapter 263. Early on, Southwest Wildlife Protection Association V: On the evening of July 10 of...; later, the chapter leans on They discovered dozens of severely injured and dead wild animals,....
Look to Chapter 250 for the clearest answer. It begins with The knowledge that several guests were soon returning had fans arriving at..., keeps building through Among them, Su Yinwan's fans were the craziest., and lands on It should be at the top right now." Hearing this, Su Yinwan finally had.
Chapter 247 is the strongest chapter-level answer because it starts from Facts have proved that arch-enemies often understand each other the best. and follows through on Why should he expect food without contributing?] [Support!.
If you want the clearest chapter reference, go to Chapter 264. Early on, Jiang Li first reassured her mother, then opened the chat box with Shen...; later, the chapter leans on She had just sent a message when Shen Lan's video call came through..