My period came and an umbilical cord-looking thing came out with it, is it a possible "miscarriage"?

It's a mixture of green/yellow/brown and looks very much like an umbilical cord. However, I've not had any signs of pregnancy, so I'm not too sure what this means. Is this just a miscarriage at an extremely early stage, whereby the embryo simply bleeds as though I'm having a normal period, and the remains, i.e. the umbilical cord, comes out together with my period?