I think you may have been pregnant with twins and for some reason the second baby didn't develop. You need an ultrasound and an obsetrician to ensure that the second placenta doesn't affect the blood...
Chances are, something happened to the twin. But since the remaining baby has lots of room to grow, it will probably be born as if it were a single.
permit passage of nutrients and oxygen from the mother to the fetus
umbilical cord and fetus
you can photo shop them ...