Not at all. Completely natural. And it helps relax you, which also helps relax the baby. IF your partner cannot find you attractive (and many men do like pregnant women!), you should be able to satisfy yourself without guilt. I say go for it!

I agree with rooted. You're not disrespecting your baby in any way at all - s/he doesn't have a clue what you're doing and you're doing it to your body not his/hers. Having a good orgasm will chill you out and therefore your baby will feel nice too.

As for your partner, some men find having sex with an obviously pregnant lady a little weird. Don't take it personally. He does sound like he's got no tact though. Bet his body is just perfect hey? Yeah, thought not. Maybe he should try growing a brand new human being and then he can pass judgement.