what causes large blood clots during period
1 This lining is also shed as clots during menses. 2  Miscarriage. 3  A woman who has suffered from a miscarriage may pass large blood clots or large lumps of tissue. 4  In case you are pregnant, it is recommended to go to your physician immediately if you happen to pass large blood clots from your vagina. 5  Enlarged Uterus.