Fetal blood loss from vasa praevia

**Definition:** In vasa praevia, the fetal blood vessels connecting the placenta and umbilical cord cross the internal cervical os, the entrance to the birth canal, underneath the fetus. These vessels are more liable to be injured by instrumentation (e.g. scalp electrode, intrauterine pressure catheter, vaginal exams) or simply due to the normal mechanical forces of labour leading to serious fetal blood loss.