Velamentous Cord and Vasa Praevia

Two findings that are often mentioned together

A velamentous cord insertion means the umbilical cord attaches to the membranes surrounding the baby rather than directly into the placenta, so the vessels run through the membranes for a distance before reaching placental tissue. On its own it is a variation in anatomy, and many pregnancies with one are entirely uneventful.

Vasa praevia is what happens when those unprotected vessels lie in the wrong place. RCOG Green-top Guideline 27b defines it: "Vasa praevia occurs when the fetal vessels run through the free placental membranes. Unprotected by placental tissue or Wharton's jelly of the umbilical cord, a vasa praevia is likely to rupture in active labour, or when amniotomy is performed to induce or augment labour, in particular when located near or over the cervix, under the fetal presenting part."

The guideline classifies it into two forms: "type I when the vessel is connected to a velamentous umbilical cord, and type II when it connects the placenta with a succenturiate or accessory lobe." So a velamentous cord is the anatomy behind type I vasa praevia — related, but not the same finding, and a velamentous cord away from the cervix is not vasa praevia at all.

The numbers that explain why it is taken so seriously

RCOG describes the condition as "uncommon in the general population with a prevalence ranging between 1 in 1200 and 1 in 5000 pregnancies, although the condition may have been under-reported".

The outcomes split entirely on whether it was known about in advance. The guideline states that where it presents unexpectedly — "by the presence of dark-red vaginal bleeding and acute fetal compromise after spontaneous or artificial rupture of the placental membranes" — "the fetal mortality rate in this situation is at least 60% despite urgent caesarean delivery. However, improved survival rates of over 95% have been reported where the diagnosis has been made antenatally by ultrasound followed by planned caesarean section."

RCOG's patient information puts the same risk in plainer terms: the vessels "are very delicate and can tear when you are in labour or when your waters break. This is very dangerous as the blood that is lost comes from your baby. Babies only have a small amount of blood in their bodies so they don't need to lose much to become very unwell or even die. Up to 6 in 10 affected babies can die if this happens."

There are very few conditions in obstetrics where knowing in advance changes the outcome that dramatically.

Who gets looked for it

The UK does not universally screen for vasa praevia at the 20-week scan. RCOG's patient information sets out who is offered a closer look: "If your placenta is low, if you are carrying more than one baby or if your placenta or umbilical cord develops in an unusual manner, you are at higher risk of having vasa praevia. You may be offered an extra scan during your pregnancy to check whether you have this condition."

A velamentous cord insertion, a bilobed or succenturiate placenta, a low-lying placenta, IVF conception and multiple pregnancy are the situations that prompt it. The examination is a transvaginal ultrasound with colour Doppler, which shows blood flow in vessels crossing the membranes near the cervix.

This is why a report mentioning a velamentous insertion matters even though the insertion itself may be harmless: it is the trigger for looking somewhere specific.

If vasa praevia is confirmed

The plan is a planned caesarean before labour starts. RCOG's patient information: "If you are found to have vasa praevia before you go into labour, you should be offered a planned caesarean at around 34-36 weeks of pregnancy."

Because that is preterm, steroids are part of the plan: "As this would mean that your baby is being born preterm, you would be offered a course of steroids (two injections, 12-24 hours apart) to help mature your baby's lungs and other organs."

Some units admit women with confirmed vasa praevia to hospital in the weeks before the planned birth so that an emergency caesarean can happen within minutes if the membranes rupture. Practice varies and depends on how far you live from the hospital and on your individual picture, so ask what your unit plans and why.

What to do if something happens before then

Any bleeding, any leaking of fluid, or any contractions need immediate attention — not a call in the morning, and not a wait to see whether it settles. RCOG's guidance is that if vasa praevia is suspected when labour starts or the waters break, "your baby needs to be born urgently. Usually an emergency caesarean would be recommended."

Make sure your notes and your handheld records say vasa praevia clearly, and that you know which number to ring and which entrance to use out of hours. If you attend a hospital that has not been managing your care, say the words vasa praevia at the door, because it changes the response immediately.

A velamentous cord without vasa praevia

If the scan found a velamentous cord insertion and specifically excluded vasa praevia, the picture is much less dramatic. The remaining consideration is that a cord attaching to the membranes can be associated with less efficient transfer to the baby, so some units add growth surveillance.

Ask directly whether vasa praevia was looked for and excluded, whether growth scans are planned, and whether anything changes about how you give birth. In many cases the answer to the last question is no, and being told that clearly is worth the appointment.