It's far higher than that, but most miscarriages occur so early that in the past, or today if not actively checking if you are pregnant, a woman wouldn't have known it happened. This is obviously difficult to study, but current thought is that miscarriages occur in 30-50% of fertilizations, and with more and more tracking, people are more and more likely to know about it.

This was our experience, having a positive pregnancy test and then my wife getting what we would have thought was just a late, heavy period shortly afterward.

Early testing is nice, but with subsequent attempts to get pregnant we chose to wait quite a bit longer after a missed period before doing a pregnancy test, because we didn't want to go through the roller coaster again.

You raise a good point. Many are not aware how common miscarriages are. I don't know if it would make it any easier to know they happen often to many couples but it might make it easier to prepare.

I wouldn't be surprised if the majority of women who have tried to get pregnant have had at least 1 miscarriage in their lifetime. Fertile or not, it appears to be part of the child-bearing process given sufficient attempts to reproduce.

1 in 4 pregnancies was the figure I was quoted, when my wife had a miscarriage.

1 in 4 known pregnancies. Most miscarriages occur before pregnancy hormones able to be detected. Probably around 40-60% of fertilized eggs die.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5443340/