If it is bothering you, then you should say something, even if it means bringing it up again next time. It could be a useful way to explore how you feel about bodies and periods and who knows what else. I bet your T will be curious to know how you feel and not upset or embarrassed. I have talked about all sorts of random things that come up for me, including noticing when my T went into her office with bare legs and came out wearing nylons and another time when I felt uncomfortable that she was going on a honeymoon because it is basically a sex vacation (talk about awkward!). I believe these sorts of things that bring up seemingly disproportionately intense feelings are all "grist for the mill" in therapy.