Obstetrics

Vasa praevia

Unprotected fetal vessels run through the membranes over or close to the internal cervical os; if the membranes rupture, the vessels can tear and cause rapid fetal exsanguination.

Definition

Vasa praevia is the presence of fetal vessels running through the membranes over or close to the internal cervical os without the protection of the umbilical cord or placental tissue. It is usually associated with a velamentous cord insertion or vessels between placental lobes and can cause fetal exsanguination when the membranes rupture.

First principles

The haemorrhage is fetal

In vasa praevia, fetal vessels run through the free membranes without the protection of Wharton jelly or placental tissue. They are usually related to a velamentous cord insertion or vessels between placental lobes. If the membranes rupture across them, the bleeding can be fetal and rapidly life-threatening even when maternal observations are initially normal.

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