Lots of people have way more trauma than you and it’s quite shitty to think that you have it worse than anyone else, because you don’t.
You chose to get pregnant when you had sex (this is what we tell men all of the time).
Its absolutely fine that’s you’re having another baby but you’re acting surprised that that means you’ll have to leave your son sometimes.
You need a find a way to cope with leaving him and not feeling guilty because it’s very possible you’re going to have to stay in hospital after the birth of your second.
Ring the hospital and ask if they can both come in.
If they say no, then it’s a no.
Whats more important, having your DH there or not leaving your child with someone else?
If you need your DH there then try and get childcare or rearrange the appointment (may not be possible).
If it’s that you don’t want your son left with anyone/you don’t have childcare then get DH to look after him.
The best solution would be for DH and DS to come with you but wait outside.
Then your son doesn’t need childcare and if it is bad news and you need support then DH will be just outside of the door.