This is something I've been thinking about too. This is all anecdotal, of course:

My menstrual cycle affects my mood significantly. I tend to have mood swings, become emotionally reactive and just feel more intensely. This emotional state is so distinct from my normal mindset that whenever I start feeling that way I think "looks like I'll be getting my period soon...". This usually starts a couple days before my period and ends a couple days after it starts. I don't associate this with my bipolar symptoms, but I think it does indicate that my moods are sensitive to hormonal changes.

Earlier this summer, I had the first hypomanic episode that I've had in a long time. The first half was a euphoric hypomania and it ended in dysphoria and then I went back to normal. I had a stretch of normalcy for the next few weeks. Then the very first day of my last period, a bit over two weeks ago now, I went straight back into my hypomanic state - the bad kind. I've also noticed this sort of pattern happening before with my period and depressive episodes.

So I think what I'm trying to say is that periods don't normally trigger bipolar episodes in me, even though they do cause mood fluctuations. However, if I'm already going through a time where I am susceptible to bipolar episodes, I think my period can trigger relapses and intensify symptoms.