This is a horrible and shocking betrayal. No way round that. He's told someone when he agreed not to, over shared information that isn't about him but about you - and not even told you he's done it - and is laughing along when someone who is nothing to do with you and not known or trusted by you makes vile toilet and worse jokes at your expense. He should be ashamed of himself!
I woukd suggest starting by re-affirming with him that nobody outside the close family and friendship group you agreed to tell knows about the pregnancy. Count them off on your fingers as you name them and ask him directly whether he has already told anyone else or plans to. And is he sure? Nothing has been let slip accidentally? Is there anyone he wants to tell is the next question. Get him to think hard. Is there anyone he wants to tell, perhaps to get support?
If he doesn't confess or mention this woman, he is a deceiver as well as a betrayer.
Ask him if he is happy and feeling positive and excited about the pregnancy and of he has any worries about you, your health or his transition to fatherhood. Give him a chance to get anything out.
It's your decision then either to keep silence or to tell him he needs to close his laptop so you don't get hurt by seeing the truth about his behaviour and attitude.
If you tell him what you've seen, ask him to shut down all personal talk about you between them. Ask him how he'd feel if he discovered you were blabbing to a new friend or colleague he didn't know about his genitals and intimate details of them and laughing along at jokes about him losing control of his bowels in public.
It just has to stop, doesn't it? Are you having his baby or just providing subject matter for offensive jokes to entertain him?
Last question (for him and you): Are these the actions of a loving supportive husband? How loved and supported does (he think) this makes you feel?
He then has a chance to try to put things right. I hope he does.