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The Placenta: Low-lying, Separating and Vasa Previa

By: Rachel Newcombe - Updated: 22 Jul 2010 | comments*Discuss
Placenta Nutrient Baby Womb Pregnancy

The placenta is the organ that attaches the foetus to the womb and links the blood supply of the mother to the baby. It enables a supply of vital nutrients and acts as a lifeline for the baby as well as producing essential pregnancy hormones. But sometimes things can go wrong with the placenta. Some of the main complications and placenta-associated conditions are a low-lying placenta, separating placenta and a rare condition called vasa previa.

Low-Lying Placenta

The placenta is usually found in the top part of the womb, but in some instances it forms in the lower half. When it forms low down it partially or completely covers the cervix, effectively blocking the way out of the womb. This situation is what’s known as a low-lying placenta, or placenta praevia.

Ultrasound scans can reveal the position of the placenta and in many cases scans in the first trimester reveal a low-lying placenta. This generally isn’t anything to worry about as up to one in four placentas are low-lying in the early stages, but move as the womb expands and get back in the correct position. A further scan later on, between 32-34 weeks, will confirm its new position.

However, up to 1% of placentas are still lying low at the end of pregnancy and this can cause difficulties. Sometimes they’ll be no adverse symptoms at all, but the position can cause bleeding. If this happens, it’s crucial to see a doctor and, depending on the severity of the bleeding and your stage of pregnancy, you may need to stay in hospital and have a caesarean section.

Separating Placenta

The placenta is usually attached to the wall of the womb until after you give birth, but in a small amount of cases it can become separated before that time. When the placenta becomes loose and detached, the term used is either a separating placenta, or it may be called a placental abruption, accidental bleeding or accidental haemorrhage. Although different names, all of these refer to the same condition.

The amount by which the placenta becomes separated varies, from a small detachment to the whole thing coming loose. It can occur at any point in your pregnancy, from mid-pregnancy onwards. The cause isn’t always clear cut, which is why the terms accidental bleeding or accidental haemorrhage may be used, but common causes include high blood pressure, under-nourishment, falling, smoking, or taking recreational drugs.

The most common sign that this has happened is sudden heavy bleeding, although bleeding can occur internally too, accompanied by lower abdomen pain and cramping. Other symptoms such as dizziness, a rapid pulse and a week feeling may occur. If you experience any of these symptoms, or have any other health concerns, it’s crucial to see a doctor, especially if you have bleeding.

In the case of slight bleeding and a partially detached placenta, you may need to stay in hospital for a couple of days until the bleeding stops. If it’s severe and the baby seems to be distressed, it may be necessary to have an emergency caesarean section. In cases where the placenta has become fully detached, it does pose a risk to the life of your baby.

Vasa Previa

Although relatively rare, vasa previa (or praevia) is a condition that occurs when the foetal blood vessels are situated across the entrance to the birth canal and rupture when the cervix begins to dilate at the start of birth or during labour. The rupturing causes haemorrhaging and it can be devastating, as the baby finds it extremely difficult to cope with the effects.

It can sometimes be picked up by scans, but sadly the condition often lies unnoticed until late pregnancy and in 70-90% of cases it isn’t known about until it happens.

The risk of vasa previa occurring is increased if you have any of the following:

  • A low-lying placenta
  • Multiple pregnancies
  • A bi-lobed placenta with two sides
  • A placenta with more than two lobes (succenturiate-lobed)
  • A pregnancy resulting from IVF
  • A history of uterine surgery
  • A history of painless bleeding, at any stage of pregnancy
If your circumstances match any of these and you’re concerned about the risk of vasa previa, speak to your doctor. There’s a scan called a colour Doppler ultrasound which can be used to measure the velocity of blood flow in the womb and it can diagnose the presence of vasa previa. For more information, visit the Vasa Previa Support Group website.

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