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Placenta Praevia

placenta; praevia; previa; bleeding; bleed; blood; loss; uterus; ultrasound; cervix; haemorrhage; caesarean; section;

The placenta is an organ within the uterus (womb) through which the unborn baby gets nutrients (food) and oxygen, as well as removing waste products. It is attached to the wall of the uterus by many blood vessels.

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What is placenta praevia?

The placenta is an organ within the uterus (womb) through which the unborn baby gets nutrients (food) and oxygen, as well as removing waste products. It is attached to the wall of the uterus by many blood vessels.

Normally, the position of the placenta will move as the womb grows and stretches, so that eventually, by the last three months of pregnancy, it should be near the top of the womb.

In some cases however, (one in 200 pregnancies) the placenta stays in the lower portion (part) of the womb, and either partially or completely covers the cervix (neck of the womb). This is known as placenta praevia.

Placenta praevia occurs in four grades, ranging from minor to major:

    • Grade 1 – (minor) the placenta is mainly in the upper part of the womb, but some extends to the lower part.
    • Grade 2 – (marginal) the placenta reaches the cervix, but doesn't cover it.
    • Grade 3 – (major) the placenta partially covers the cervix.
    • Grade 4 – (major) the placenta completely covers the cervix (most serious type of placenta praevia).

What causes placenta praevia?

Often there is no obvious cause for placenta praevia, but the placenta may develop lower than it should because:

    • there is a large placental area (eg. with twins)
    • there may be scarring of the lining of the uterus from previous caesarean or curette
    • there may be late implantation of a fertilized ovum (egg)
    • smoking may increase your risk (cause unknown)

Nothing you do can change placenta praevia. Only growth of the womb over time can improve the position of the placenta.

How will I know if I have placenta praevia?

Placenta praevia is usually picked up with an ultrasound between 18-20 weeks. If a "low lying placenta" is found, a further scan is done at 32 weeks to see if the placenta is still low. Only two to five percent of placentas that are "low lying" on the early scan become placenta praevia grade three or four later in the pregnancy.

The signs and symptoms

    • Sudden, painless, bright red vaginal loss, usually in the later half of the pregnancy
    • Painless vaginal bleeding after sex
    • Uterine cramping with bleeding
    • Bleeding during labour

Placenta praevia is the most common cause of painless bleeding in the last three months of pregnancy. Bleeding occurs because of growth of the lower part of the uterus, which stretches and thins to make room for the growing baby. This may cause the placenta to tear at the edges, resulting in bleeding (your blood, not your baby's).

What do I do if I have a bleed?

Any vaginal bleeding, when you're pregnant, should be checked by your doctor, or at the hospital. Bleeding doesn't always mean placenta praevia. The bleeding may be due to another cause, eg from the cervix, a normally positioned placenta, or there may be no obvious cause.

What happens at the hospital?

If the grade of placenta praevia is minor, and the bleeding has stopped, you may be able to go home. You will need to live, or be close to, the hospital with access to transport because if you have another bleed you will need to return to the hospital. You may also need to avoid sex. Discuss this further with your doctor or midwife.

If the bleed is heavier, you will need to be admitted to hospital. You may need an intravenous drip (a plastic tube in your arm), and have your blood taken, to check your haemoglobin (iron level) and blood group.

Your blood will be taken each week so that an exact match is always ready, and donor blood will be kept available in case you need a blood transfusion. The doctor may want you to take iron tablets if you have anaemia (low blood haemoglobin level).

If you have a negative blood group, you will need an injection of Anti D. This is given so that your baby is not affected by the bleeding.

Your baby may be monitored with a cardiotocograph (CTG) to make sure your baby is not distressed. This usually takes 10 to 20 minutes, but may take longer. The CTG records your baby's heart rate and response to movements and contractions.

If you are less than 34 weeks pregnant, Celestone (steroid) injections are given to help your baby's lungs to mature, in case of an early birth.

Being in hospital doesn't stop you from bleeding, but your baby can be delivered more quickly if needed.

When the bleeding has settled, you will be able to walk around the hospital and/or grounds, as long as you tell the staff where you are going. Talk to your doctor or midwife about day leave; this may or may not be appropriate for you.

Doctors or midwives will discuss your test results with you, and what action will be best for your and your baby's health.

Do I have to have a caesarean?

Sometimes when women have a minor grade placenta praevia (grade 1 or 2) it is possible to have a vaginal birth. Grades 3 and 4 placenta praevia need a caesarean.

An anaesthetist will talk to you about the most suitable anaesthetic to have. If your placenta is at the front of the uterus, you may be advised to have a general anaesthetic, as there is usually more bleeding at the time of delivery. Otherwise, an epidural or spinal may be considered.

How dangerous is a placenta praevia?

You may not bleed at all throughout your pregnancy, but placenta praevia can be potentially life threatening, as it is possible to lose your entire blood volume in 10 minutes. That is why you need to stay in hospital, close to emergency facilities.

Reference

Women's and Children's Hospital (South Australia) 'Placenta Praevia' 2010

Further reading

Medline Plus (US National Libraries of Medicine) 'Placenta Previa' 
http://www.nlm.nih.gov/medlineplus/ency/article/000900.htm 

PubMed Health (US National Libratries of Medicine) 'Placenta previa' 
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001902/

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The information on this site should not be used as an alternative to professional care. If you have a particular problem, see your doctor or midwife.

 

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