In my experience, I found they don't like it too deep, and you don't feel as if you are going deep when they are up the duff.
They don't want you basting the baby.
Tits swell quite nicely though.
And yes some do get horny. This lady says she does.
She looks less than 6 months gone.
But if you haven't tried it give it a go you might become a pregaphile.