Almost all miscarriages are unexplained. Because research into health issues that primarily affect women is still in the fucking dark ages.
I had a friend who suffered multiple miscarriages (including one that wouldn’t complete itself and almost required surgical intervention because she was bleeding so badly - a procedure that her home state of Ohio is trying to ban now because it’s the exact same procedure that is used in electric elective abortions.
After so many losses they finally figured out that her progesterone levels were extremely low and supplemented progesterone the next time she got pregnant. She now has a healthy baby boy as a result.
Medicine doesn’t even have solutions for so many of these problems, and half the government wants to take away one of the few tools available to us to keep women alive and healthy.