two vessel umbilical cord

I am currently thirteen weeks into my 4th pregnancy.I have a normal healthy three year old boy.I have also miscarried 2 spontaneous trisomy 13 pregnancies last year.I had my twelve week scan  on monday which essentially showed a normal looking fetus which was spot on size for dates and showed no physical abnormalities for any chromosomal abnormalities.however they did find that I have a 2 vessel umbilical cord.I was reassured that this is just a normal variance and that I shouldn't worry,But i have since read up info about this condition on the net and am now quite concerned about this pregnancy.My maternal blood biochemistry was also normal and showed a low risk for any abnormalities.I am having another ultrasound at 16 weeks just to check fetal growth.Should I be worried?