Single Umbilical Artery / 2 vessel cord

Does anyone have any experience or info about this?? 
So I had my NT scan today for my twins (12w) and the perinatalogist was concerned that both babies might have a problem with the development of heir unbilical cords resulting in one artery and one vein instead of two arteries and one vein. She said it's still possible they don't and she's having me come back at 15w, 18w and the babies will also have echocardiograms (heart ultrasound) at 22 weeks. 
I'm still waiting for my genetic screening results, she said that this condition could be associated with chromosomal defects (trisomy 21, 18 or 13), placenta problems, restricted growth, and possible heart or kidney abnormalities as well. One of the babies is still smaller and less active than the other and apparently it's too soon to know if we need to be concerned about that yet. 
I was reading some stuff online and the possibilities are pretty terrifying, including higher risk of 2nd trimester miscarriage, low birth weights, prematurity and problems during delivery. I'm having twins so already at risk for prematurity, low birth weight and delivery problems, so now I'm extra worried about what might happen. I'm trying to think positive and not freak out, but I'm worried :(