Hi, B.!
Congrats on your pregnancy! I have a son who also had a 2-vessel cord and I found out about it at my routine 20-week ultrasound. My doctor explained to me that the main risk associated with this is having a small-birth-weight baby because instead of having two "lines" in for nutrients and one line out, they only have one of each. Because of this small risk, he made sure to measure me carefully each time and when I measured under one day, I was promptly ushered over to an ultrasound and it turned out that everything was fine. They are looking to make sure that the baby has enough "output" (so measuring your amniotic fluid) to make sure that the baby's kidneys are functioning well.
There is also a tiny, tiny chance of having a baby born with cleft lip or cleft pallet. Both of these require surgery when the child is old enough, but it's something that they fix and then you move on and your child never even remembers that they were born with it. I was adamant about breastfeeding and my doctor said I should still be able to even if one of these happened.
My son was born a week late and weighed 8 pounds. He had his kidney's checked right away (routine with 2-vessel cord babies) and they were fine. He did not have cleft lip or pallet and is perfectly normal from head to toe.
I have since known two other mommies with this same issue in their pregnancy and both of those babies have been born at a healthy weight near their due dates with no issues.
I hope this helps you sort through some of the "muck" you can find on the internet! Good luck!