If you have married friends or friends with kids, its probably best not to joke about when they're going to pop one out. Fertility can be long, expensive, and not very fun.
Answer: very†. But it often isn’t talked about.
And, I strongly agree, not talking about it is very Bad indeed.
Ironically, I think developed nations’ success in all but eliminating premature deaths from once-ubiquitous infectious diseases has left recent generations without the highly-practised coping skills, social support systems, and painfully resigned stoicism that helped get our great-great-grandparents through the horrible inevitable process of burying half their kids before the poor little bleeders could even make it to adulthood.
We’re all now such strangers to death we’re shit-scared by even the thought of talking about it, never mind directly facing up to it ourselves.
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† Even assuming the hosting part works perfectly, the whole DNA splicing and replication process is always an absolute crapshoot‡.
‡ And, to be fair, if it weren’t for all those accidental copy errors none of us would be here now to argue the issue, for life on Earth would never have advanced beyond the single cell. So yay for an imperfect process, but—bloody hell—is it one harsh SOB.
I often say things like "people should talk about this kind of stuff more because it would help them through it". I obviously mean it in a general sense (very much not trying to get specific people to talk about specific problems). Responses vary from an insincere "yeah..." to the rather odd "you can't tell people what to do".
(Edit: I'm not wanting to say that a miscarriage is a small misfortune. No, it's not. But there are many many worse things which can go wrong.)
Survivorship bias is such an amazingly powerful force on our mental models of how the world works.
Without that knowledge, when it happens there's the immediate fear that there's something wrong with you, that you'll never be able to have kids, that it's hopeless. When in reality it happens a lot, including to countless couples who go on to have big happy families.
They say if we were able to track 'unrecognized' pregnancies, the total rate of miscarry across all pregnancies is likely much higher than 25%
Cannot stress this enough. If a couple is childfree by choice they'll probably tell you. If they don't talk about whether they want kids or not, you shouldn't raise the topic.
If you’re close enough with someone to talk about intimate topics, say, sex, baby making plans are ok for discussion.
Back off if the person doesn’t want to talk about it.
But we are an open society, and part of that is talking about things.
https://expectingscience.com/2015/08/26/lies-damned-lies-and...
but is mostly quoting numbers conditional upon having detected a heartbeat. That first check is pretty terrifying. My anecdata matches yours: lots of miscarriages in immediate social groups.