He could initially be in disbelief. However, as the reality sinks in, Sasuke would start to show his softer side. He might be more attentive to Sakura's needs, like making sure she eats well and rests. He would also start thinking about how to train their child to be a strong ninja in the future, while also wanting to give the child a more peaceful life than he had.
Sakura would probably be initially very angry. She has strong feelings for Sasuke, but kidnapping is a very extreme act. So she would likely fight back, using her medical ninjutsu skills and combat abilities to try and escape.
Another reaction could be that Sakura tries to follow Sasuke. She believes that she can change his mind or that she can be of help to him. She might leave her own responsibilities behind for a while to chase after him, thinking that their bond is strong enough to overcome whatever is making Sasuke leave.
Sasuke would likely be initially shocked. He's a man who has been through a lot and is used to a life of solitude and danger. But then, a sense of protectiveness would kick in. He'd become more vigilant about the safety of Sakura and their unborn child. He might also start to think about how to be a better father than his own was, in some ways, trying to break the cycle of his family's past.
Sasuke might initially be shocked. He has always been a bit aloof and focused on his own goals. But once the shock wears off, he would probably feel a sense of protectiveness over Sakura and their unborn child. He'd start to think about how to keep them safe in the dangerous ninja world.
In some fanfics, Sasuke might initially be shocked. He could then feel a mix of joy and fear. Joy because he's starting a family with Sakura, but fear because of the responsibilities and potential dangers that might come with it.
In such a fanfic, it might explore the challenges they face. For example, Sasuke's past actions might make some in the village still be wary of him. But Sakura's pregnancy could be a symbol of hope and new beginnings. It could also show how their friends like Naruto react to the news. Naruto, being Sasuke's long - time friend, would likely be overjoyed and offer his support, while also teasing Sasuke about becoming a dad.
Sakura might initially be a bit annoyed by Sasuke's possessiveness. She's a strong - willed woman, after all. But she also understands that it comes from his love for her and the baby. So, she may tolerate it to some extent.
She might be initially heartbroken. Sakura, being in love with Sasuke, would surely be deeply affected when he neglects her. She could become withdrawn herself, losing some of her usual cheerfulness.
On the other hand, Sasuke could be very stoic about it on the surface but internally be in turmoil. He might start to analyze his own actions and whether he had missed any signs from Sakura. He could also be the type to immediately start thinking of ways to win Sakura back if he realizes he can't stand the thought of her with someone else.
There are fanfics where Sasuke is a bit more reserved in his reaction. He may not show extreme emotions outwardly but instead, internally he's filled with a mixture of excitement and fear. He might start thinking about all the responsibilities that come with having a child and how his life as a ninja will need to change to accommodate this new addition to his family.