I'd say that it might be difficult to keep it from your husband, and it may impact on your relationship if you lie, if you discuss it with him and he absolutely refuses to consider the idea, is the relationship basically being impacted anyway?
You should both agree to having another child, and if you don't, then it's not the right time, is it? And if he doesn't respect that, and uses emotional blackmail to make you continue with the pregnancy, then that's not good either.
I think the best result you could hope for is a very difficult conversation with DP explaining the situation, having the termination, maybe get some relationship counselling if this and the redundancies is making things rocky, and hoping that this is not going to end the relationship?
The alternative is lying, DP grieving for the loss, somehow DP is suspicious or finds out that it was a termination, everything implodes and things become very messy.
If there were absolutely no chance of DP finding out, I'm about eighty percent sure I'd go for withholding the truth, but only after correct procedure (counselling for sure!) and being very sure it was what was necessary. However, I think it might be very difficult, there could be a lot of guilt to carry, or worrying about DP finding out, and it would definitely be very stressful to carry out.
It's all very well hypothetically making the decision though, you and DO are the only ones who will have to live with this decision, so you must absolutely do what you feel you need to in this situation, and don't let anyone else tell you that you are wrong, because that's something that only you can decide, and it's only you that has to take responsibility if things go wrong.
You sound like you are in a very shitty situation right now. Don't make any impulsive decisions, and consider that even if talking to DP is very difficult, it would mean not having to go through this all by yourself. x