My partner and I had our worst rows when I was pregnant with our first child.
I know I was sometimes irrational and over-emotional, and the nesting instinct made we want to get things sorted when he thought we had loads of time.
He was incredibly insensitive and selfish, and did nothing to make me feel better.
We muddled through, and talking about that time afterwards he admitted to huge amounts of fear about impending responsibility, being a father, financial responsibility etc. He also told me that he was scared of what I was becoming too. I'd changed from a cool, calm independant person into a very emotional mess who cried a lot.
We're still together 5 years and 2 children later so it all got better, but i wish we'd been able to talk before. I found the pregnancy and the first 6 months very difficult because we weren't honest with each other about how we were feeling, so we couldn't share all our irrational fears of which there were many. We also had to learn to ask each other for cuddles because we realised that neither of us could read minds.
I think if you can get him to talk - tell him how you're feeling, admit to your own irrationality and other pregnancy madnesses that you're having. Try and laugh about some of your own moods so he can then feel comfortable about admitting to his own. He may be as scared as you, but it sounds as if his way of dealing with it is to be mean and insensitive to you as my partner was to me.
Your baby's nearly due so it would be great to sort it out now so you can concentrate on all the new exciting and scary things about parenthood together. We have a fabulous relationship now - I hope you sort yours quicker than we sorted ours.
Good luck. The children are definately worth it.