Considering having sex with a pregnant woman as having sex in front of your children is just weird - the fetus does not have the ability to comprehend or remember anything. You might as well feel bad about having sex at all, due to the 99% likelihood of having micro-critters on you.
There are a number of good reasons to not cut the sex during pregnancy:
- Your wife / partner is in a difficult emotional state. Weird changes happen to her body and mind, and she is vulnerable to depressions. Sex is a good way of feeling closeness and love, and thus help her go positively through the experience.
- If you don't have sex during pregnancy, you are probably going to go for over a year without 'getting any', as a new mother is often too worn out to want sex for least the first few months after the birth.
- "Not getting any" strongly increase the risk of the temptation of adultery becoming too strong. This will severely hurt your partner if discovered, and could easily break your relationship or marriage.
I do not see these risks and losses as worthwhile just to cater to a prejudice; it is possible to manipulate your own feelings to change prejudices.