My Mallard duck egg has a very large blood ring. Though yesterday that same br was there, and a heart beat?

My Mallard duck egg has a very large blood ring. Though yesterday that same blood ring was there, and the embryo had a heartbeat. I don't know if the blood ring is actually one of the veins? It doesn't look like one of veins? I'm a newbie to egg hatching so I'm REALLY concerned. Anybody have an explanation or diagnosis?