Hi lollysitx, I've come to this thread late but wanted you to know I have been in exactly your situation. I found out I was pregnant with number 4 just after we'd had our visa accepted to move to Australia. We had even ticked a box somewhere on the application saying we weren't planning any more children! I really wanted a third, but not a fourth, and had treasured every baby moment with ds3 because I believed I wasn't going to have any more. I had given away most of our baby stuff after ds3 had gone through each growth or development stage.
I felt so stupid getting pregnant with number 4, but after the initial shock both dp and I realised we couldn't go through with an abortion. I think it took a couple of weeks before we both agreed, though.
And in a way it has made it easier moving to a new country. Ok, I don't feel settled here yet, and I wish I had close friends and family around me, but sorting out my maternity care has given me something to do with my time!! And the boys have been so good about it. Ds3 keeps stroking my tummy and saying 'when the baby is born I will cuddle it and sing to it'.
I hope your dh comes round, I expect he will. I think the scans make it easier for men to appreciate that you are really growing another person inside you. It's lovely that you have felt the baby move. :) I can understand why he was bothered that you told your friends, though. He'd probably prefer you left the announcements until he had more time to come to terms with it himself.
And re. the comments, well of course I've had a load of the 'hoping for a girl?' ones (even from my own mum...) but people haven't really said anything about us being irresponsible. It's more the 'oh you are brave' comments. I tend to say, 'not brave, just foolish!' 
I still have to work on dp regarding the vasectomy...