Personally, I think it's rude to touch a person's belly without permission, a person's child (except in the case of reacting to emergencies), or a person's pet. Touching someone's dog without permission is both rude and dangerous.

I wonder if there is a market for pregnancy clothes that comes with spikes sticking out.

On a side note, people sometimes touch me without pernission too, as a reaction to my cane. Apparently having medical problems that make me require more careful handling inspires people to grab me without asking, usually in harmful ways. Sometimes I don't have that much faith in humanity. But then I grew up in a place that was very big on personal space and not touching strangers.

Oh yes, in my case the people are definitely trying to help. None of them have helped. One has hurt. Most slow me down (grabbing the arm holding my cane just means I can't walk; it does not help in any way). Unless they perceive an active emergency (and I think the one case where I was hurt, she may have thought I was going to fall, even though I was just unsteady in getting up, but she could have let go after I was standing), people should ask first. And in the case of a pregnant woman, there is no reason not to ask if it's okay first. I dunno, it just doesn't seem that hard to ask first.