I disagree with this as a blanket statement.
I am 7 months PG and haven't lost interest in sex. The fact that I am showing and have a belly have not impacted my sex life at all.
A PG woman can have sex on the way to the delivery room if there are no other complications (medical concerns).
Everyone is different, some women want sex the whole time, others lose their sex drive. Some men find it sexy, others don't. I could care less what other people think as long as my husband still finds me attractive, and he does ... so I am happy (and so is he).