Only a 2-vessel cord....

At a regularly scheduled ultrasound, the technician spent a rather long time taking pictures of the umbilical cord for Baby B. After consulting with the doctor, we were alarmed YET AGAIN with the news that Baby B only has a two vessel cord. Most babies have three vessels: two arteries and one vein. Our guy only has one of each. What does this mean?!?! Should we be in a panic? Basically, it means that he's not getting as much nourishment as Baby A. They were both doing very well at the last ultrasound; they were very close to each other in size. But, today, B is weeks behind A in weight/height. He's just a teensy little thing! Could this have been prevented? No. Can we change anything? No. Could it cause an early delivery? Yes. If he starts to be in distress, I will be induced.