usually there are 2 arteries and 1 vein. i have the knowledge of only one case. i have a friend who had a baby with a 2 vessel cord. he was born at 26 weeks. he has had numerous complications. he had a cleft palate, heart problems, stomach problems, mental retardation and alot more. he is now 5 and doing well considering all that he has been through. they said he would never be able to sit, crawl, or walk. and he can sit and crawl the fastest i've ever seen.
and i'm sure he will walk one day. he also has a feeding tube in his stomach, he has never eaten anything by mouth. he has had numerous surgeries on his heart. and although he can't talk, he understands alot of what you say. he is very sweet and affectionate.
and as far as i know i think dr.s relate most of his problems to the 2 vessel cord.
so i'm sure your friend will have a long road in front of her. just be there for her. like i said, this is the only case i have ever heard of, so all may not be that severe. and i think it matters that they know before, because i don't think they knew with her baby, that is why he was born so early. so there may be things they can do in utero. lets hope so.
i will keep them in my prayers.