First of all, forget what "most of your friends say they were doing" during their pregnancies. Every man and woman experiences pregnancy and sex differently. You need to get the bottom of his feelings and attitudes. Tell him you understand his concerns about potentially harming baby and you'd like him to get reassurance from your healthcare provider. Either bring him along for your next appointment or call the office and the staff can discuss this with him down the phone. Or, buy a pregnancy book that provides information about sex during pregnancy. Undoubtedly, it will reassure parents that baby won't be harmed by having sex as long as you're fit and well.
Next, explore with him if he has a belief that somehow the mother of his child should not be a sex goddess too. Many men find it hard to combine seeing their wife as a mother and a lover. If he'll open up about such attitudes it'll be easier to get him to see you as a whole woman. Certainly if you're "in the mood," stay away from talking about baby-stuff with him because that may kill the mood. Also that way he can practically ignore that you're pregnant while you're trying to get him in the mood for love. Men can get pretty good at that denial thing! Once you've come this far, dress attractively, light some candles and put some new mood music on. Hopefully he'll be able to let go and see you as a lover again.