Comment by derbOac

The problem that became very salient to me dealing with miscarriage is that women who have healthy pregnancies are also more likely to have problems with morning sickness, and are more likely to avoid things like coffee that are likely to make them feel even more nauseous. Women who have troubled pregnancies that are more likely to end in miscarriage are less likely to feel nauseous and therefore continue to drink and eat things as before.

So it's possible caffeine consumption is a sign of a troubled pregnancy rather than a cause of it. I'm sure there's a point where caffeine becomes problematic but that could be said of a lot of things.

There's a paper in NEJM or JAMA that pointed to this as a likely explanation but it's been a few years and don't have time to look for it now. I think they were looking at timing of caffeine consumption and nausea symptoms?