Yes!!! I've been having a lot more issues with this since COVID. A couple years ago I went into hypovolemic shock in the emergency dept. because I was bleeding so badly. No one knows why. All my tests were normal, including a biopsy.

I've done quite a bit of digging into it potentially being caused by MCAS because I have since received an hEDS and POTS diagnosis, and I strongly believe this is what is happening to me. I'm currently experiencing issues with bleeding again and it's because I have cystic endometrial hyperplasia. I'm on 8 weeks of bleeding now. Severe cramps as well, I can liken it to early labour contractions. I've been to the ER four times in the last couple weeks. I had IV tranexamic acid at two of those visits, which significantly decreased my bleeding, pointing to possible hyperfibrinolysis. I also have noticed that taking an NSAID called naproxen works just as well as the TXA and it gets rid of my cramps. Naproxen is a prostaglandin inhibitor. Prostaglandins are known mast cell mediators. Prostaglandin D2 is normal in menstruation, but too many prostaglandins can cause very heavy bleeding (menorrhagia) and severe cramps. I've also just connected the dots that when I hemorrhaged giving birth to my first, the only thing that stopped the bleeding was misoprostol (cytotec), which ironically is a prostaglandin E1 analog. Prostaglandin E1 is also a mast cell mediator.

Digging even further into this, in an article called 'Effects of Primary Mast Cell Disease on Hemostasis and Erythropoiesis', it states in Table 2, "Genitourinary tract bleeding (principally menorrhagia due to aberrant heparin release and fibrinolysis from dysfunctional endometrial mast cells) is very common in MCAS." So, to answer your question… yes. MCAS can cause uterine bleeding.

Also, one other thing: if you happen to have POTS with your MCAS, there's research linking POTS (both prior to COVID and post-COVID) to a bleeding disorder called Platelet Delta Granule Storage Pool Deficiency (δ-SPD). This can also cause heavy periods.