What condition is defined by the presence of fetal blood vessels crossing the internal cervical os?

Vasa previa is characterized by the presence of fetal blood vessels that traverse the internal cervical os, which poses a risk during labor and delivery. If these vessels rupture, it can lead to significant fetal hemorrhage, which is a life-threatening situation for the fetus. The blood vessels may be part of the fetal membranes and are not protected by the placenta, making them vulnerable to injury during cervical dilation or rupture of membranes.

This condition typically occurs when the fetal vessels are situated below the presenting part of the fetus, and it is critical for healthcare providers to identify it during prenatal scans to prepare for a potential emergency. Management often includes planning for a cesarean delivery if diagnosed early enough, to prevent any complications associated with vessel rupture.

Understanding vasa previa allows for timely intervention, significantly improving outcomes for both the mother and fetus. Other conditions like placenta accreta, placental abruption, and cervical incompetence involve different pathophysiological mechanisms and present distinct clinical challenges, but none feature the crossing of fetal blood vessels over the cervical os as a defining characteristic.