What distinguishes vasa previa in pregnancy?

Vasa previa is characterized by the presence of umbilical cord vessels that cross or run near the cervical os. This anatomical arrangement is critical to recognize because it poses significant risks during labor and delivery, particularly the potential for vessel rupture, which can subsequently lead to fetal hemorrhage.

In cases of vasa previa, the fetal blood vessels are not protected by either the placenta or the umbilical cord, unlike typical presentations where these structures are well-encased. This situation is particularly dangerous because if the membranes rupture, these fragile vessels can tear, resulting in a medical emergency.

Understanding the implications of vessel position is vital for managing labor and delivery safely. Therefore, identifying the presence of vessels at the cervical os is crucial for preparing for potential interventions to protect both the mother and the fetus during childbirth.

The other options do not accurately define vasa previa. Excess amniotic fluid, multiple fetuses, and low fetal heart rate may be related to other pregnancy conditions or complications but do not specifically indicate the positioning of umbilical vessels in relation to the cervix, which is the hallmark of vasa previa.