every topic is painful to someone.
If we start making the ordinary stuff of life "off limits" on the chance that someone may have a secret struggle, there would be very little friendly conversation in the world. Does not excuse the ugly attitude you encountered, but I think a taboo on pregnancy talk is just unfeasible and unreasonable.
If you're in a situation where someone starts talking/joking about a subject that you are sensitive to, I think you have three choices.
1. Ask the group to change the subject (ok but can get sticky if they want to know why and you don't want to tell)
2. Change the subject yourself (not that hard to do, I do it all the time for various reasons)
3. Excuse yourself and come back later hoping they will have moved on by then
To be honest, though, what the OP did actually strikes me as rude. One of my pet peeves is for someone to take it upon themselves to speak for me
. If I were the one who was having the fertility issues, I would not want anyone to take someone else aside and tell them to stop talking about pregnancies. I'd feel pitied and I'd feel as if that person didn't think I could take care of myself for myself.
In addition, the OP is telling the person someone's secret. Yeah, you didn't say who it was, but there's always the possibility that she could guess. And it doesn't always take knowing much about the person to be able to guess. Just in the act of telling her that someone
is having this problem, you could give away who it is by your body language. It's just not your place to take this stand unless the person has asked you to do it on her behalf.
If the OP wants the conversation to be redirected, then the very best thing to do is redirect it herself. It goes with the natural flow of conversation and it's a whole lot better than saying, "don't talk about that because someone here may be sensitive to that subject."
As for the lady's response, she was pretty insensitive, but I kinda don't blame her for not wanting to comply with the OP's request because it wasn't the OP's place to do what she did.