the vein is bigger than when you have two but when there are two they are spread out to different spots, one to each kidney, I believe. So the worry is that not enough waste is being taken away, hence the worry about birth weight and all the rest.
I just have to go with all the good stories and cross my fingers!
Now, if only we had a board like this for "SUV" (single umbilical vein) support board!
I'm off to look!