Is it abnormal to have pieces of coagulation in the menstrual blood?
It is normal to have pieces of clotted blood in the menstrual blood.
Normally menstrual blood contain some pieces of clotted blood or something that looks like small piece of blood clot. Small pieces of the endometrium sheds during menstruation, and it looks like blood clot.
But passage of large amount of clotted blood during menstruation denotes heavy menstrual bleeding. Doctors often ask the patients while taking history of menstruation : "Do you pass a lot of blood clot during your period bleeding?"