Hallows, not much help here but you have to do what you think is right.
You say your DH is determined you have a termination? Not a very helpful attitude as I assume he was there at conception & did little to prevent it.
I'm not going to come over all 'your body, your choice', as a married couple with children it has to be a descision you make together, but if he is determined you may have to make the choice alone.
I had two terminations when I was younger, pre-DCs, they were both fine emotionally, I feel no regrets as I was young & not in the right relationships.
However, married & two children & down the line I don't know if I could, I think it's something I would regret, but then, a third child.....would I regret that & feel guilty?
Tough, tough choice Hallows, can you & DH speak openly about it without intransigence on his part? I think he needs to understand your feelings more instead of being so strident. Why does he feel another child would be such a bad thing? Can he understand your objections?
Sorry I can't be any more help, I hope you find a resolution. Ultimately, do what is best for you.