Went to the doc today luckily to say I am having a boy💚💙but my doc said the baby has 2 vessels & 1…

Went to the doc today luckily to say I am having a boy💚💙but my doc said the baby has 2 vessels & 1 vein not sure what this means? The doctor told me this is very rare, so I just want to know has any other moms have this situation? My doctor tried to explain it but I'm really not understanding..