Final answer:
The critical concern with vasa previa is a) fetal mortality rate. Vasa previa is a rare condition in which the umbilical cord vessels cross or run alongside the cervix, and can result in severe bleeding and fetal distress.
Step-by-step explanation:
The critical concern with vasa previa is a) fetal mortality rate. Vasa previa is a rare condition in which the umbilical cord vessels cross or run alongside the cervix. This can result in the vessels being compressed or ruptured during labor, leading to severe bleeding and fetal distress. If not promptly diagnosed and managed, vasa previa can be life-threatening for the fetus.