Venous pool?

I went to the ER today because a near accident we had last night that left me in a lot of pain. After an ultrasound it was determined I have a venous pool of blood about 2 cm long between my placenta and uterus. I have to check in with my regular OB on Monday to see if it gets any larger.

Have any of you been told you have a venous pool of blood? What happened? They basically said it could either stay and get larger causing problems, or go away.