Final answer:
Cord Prolapse is the correct term for fetal vessels or the umbilical cord lying over the cervical os. It is a serious condition where the umbilical cord could be compressed during childbirth. The umbilical cord consists of two arteries and a vein that connect the fetus to the placenta.
Step-by-step explanation:
The term used to describe fetal vessels or the umbilical cord lying over the cervical os is Cord Prolapse. This is a critical condition during childbirth where the umbilical cord drops ('prolapses') through the open cervix into the vagina ahead of the baby. The pressure from the baby on the prolapsed cord can compromise blood flow to the fetus. It is distinguished from other conditions such as Nuchal Cord, where the cord is wrapped around the baby's neck, Umbilical Hernia, which is a bulge near the navel, or Uterine Prolapse, where the uterus descends towards or into the vagina.
The umbilical cord, which includes two arteries and a vein, connects the fetus to the placenta. The umbilical vein carries oxygen-rich blood from the placenta to the fetal heart, while the two arteries carry deoxygenated blood away from the fetus towards the placenta. After the birth, the umbilical cord is typically clamped and cut, leaving a stub that will become the navel once it heals.