2 vessel umbilical cord?

I was just told that my son has a 2 vessel cord and they want to run some more tests next week. My doctor says I shouldn't be concerned but I keep reading different stories online and I'm worried. With my 1st son I never heard about this. Mind you it was a military hospital and they feel that an ultrasound is not needed during the pregnancy so this is honestly the 1st I've ever heard of this. My 1st son is perfectly healthy and strong so no concerns there but should I be worried? I'm so scared right now that somethings wrong and I don't understand why this is the 1st time I've ever heard about this. Any info would be appreciated, thanks.