I have never experienced this before! It seemed unlikely to me that losing a little bit of the blood pumping around in your body could affect your uterine lining, which is a little different. But since I’m not a professional, I’ll defer to what our expert has to say on the matter!
I think missing your period after donating blood is more anecdotal than factual. The fluid that you lose during your period is the lining of your uterus that has been thickening but is not needed, so it really doesn’t have anything to do with any blood you may donate. And that’s why we have medical experts here, so be sure to read what Sandy has to say.
Thank you for donating blood -- our supply is always in need of generous donors like you! Donating is probably not the specific cause of your period being late. Although because it is true that stress (physical or emotional) can definitely lead to a late period, I would say that it could be a contributing factor. Other things to consider are changes in sleep, diet, physical exercise, infections, other hormone imbalances, and (like you alluded to) pregnancy. It is not too unusual to have a late period once in a while, but if it becomes a pattern, your PMS symptoms continue or you are more than a few weeks late, make an appointment to discuss with your healthcare provider.
I donated blood a few weeks ago (before ovulation) after only waiting the minimum time between donations and for the first time ever I fainted repeatedly immediately after, limbs going numb, etc. I'm calling it more "excessive blood loss" than "blood donation" at this point -- I needed to wait more than the minimum time. Well my period is late! I track it and once it hit the longest I've ever recorded (36 days), I took a pregnancy test (though doubtful, especially since I also had mild PMS symptoms like achy breasts, though not as much as usual) and it was negative, so I decided it was just really late. I'm at 1 week later than expected and wondering if my cycle is skipping entirely? Thought to search and see if I was the only one. I found one page that had a *bunch* of girls asking this same question and old man doctors all commenting, "No connection" well I bet there is a connection (under some circumstances) just periods are treated as taboo so it's not well documented! My guess is my body treated the too-early blood donation as a stress event, that my body couldn't support growing a baby right now, so it didn't prepare for one (the real thing going on when extreme weight loss, for example, causes missed periods)." - snikdacaras
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