on top of that, they might have had bad experiences with pregnancy and you could be reminding them of a bad time in their life
Yes. Or they could be struggling with infertility. They might have just had a miscarriage and desperately wish they were still pregnant.
Or they might be pregnant and planning to have an abortion, and not wanting to have to deal with other people’s judgmental attitudes towards abortion.
Basically, if someone is pregnant and they want people to know, they will tell you.