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placenta praevia

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Placenta previa

When the placenta implants over or near the inner opening of the cervix, the condition is called placenta praevia. The cervix is the opening of the uterus. As the cervix dilates during labour, the abnormal location of the placenta may cause heavy vaginal bleeding and keep the baby from travelling through the birth canal.

What is going on in the body?
Placenta praevia occurs in 1 out of 200 births. In about 10% to 20% of these cases, the placenta covers the entire cervix. This is complete placenta praevia. Otherwise, only part of the cervix is covered. This is called partial placenta praevia.

Vaginal bleeding typically occurs:
  • as the lower part of the uterus starts to widen and thin out as the uterus grows in the later part of pregnancy
  • as the cervix opens during labour, which tears blood vessels in the placenta
  • with trauma to the placenta, as with the pressure of the penis during intercourse
The extent of the bleeding depends upon how much of the placenta covers the cervix and how many blood vessels are torn.

What are the signs and symptoms of the condition?
Though symptoms differ, they may include:
  • sudden, painless, bright red vaginal bleeding, usually in the later half of pregnancy
  • painless vaginal bleeding after sexual intercourse
  • uterine cramping with the bleeding
  • bleeding during labour
What are the causes and risks of the condition?
A woman is more likely to have this condition if:
  • she has had 6 or more births
  • she is carrying two or more foetuses
  • she previously had a caesarean section
  • she is older than 35 years
  • the placenta is large or abnormal
What can be done to prevent the condition?
There is no known way to prevent this condition.

How is the condition diagnosed?
Every woman with vaginal bleeding who might have this condition should be hospitalised and evaluated. The bleeding may become a haemorrhage without warning.

Tests include:
  • a pregnancy ultrasound to check the placenta's location and rule out placenta abruptio, or separation of the placenta from the uterine wall
  • continuous foetal monitoring to assess the baby's well-being
  • finding the foetus's position by feeling the mother's abdomen. In about one-third of the cases of placenta praevia, the baby is lying sideways or buttocks-first in the uterus.
  • full blood counts, or FBCs, to follow the mother's blood losses
In many cases, placenta praevia causes no symptoms and detected only by pregnancy ultrasound in the early second trimester. In these cases, no symptoms may ever occur and the placenta later may become normally situated.

What are the long-term effects of the condition?
When a partial placenta praevia is found early in pregnancy, it may be managed or change so that a vaginal birth is possible. Complete placenta praevia usually calls for a caesarean section when the foetus is mature or if the mother starts to bleed heavily.

In some cases, the mother:
  • suffers blood loss and shock
  • gets an infection
  • develops an embolism or blood clot
  • must have a hysterectomy if the placenta will not separate from the uterus
While the mother is usually fine, birth trauma or a haemorrhage may harm the baby. In 15% to 20% of cases, the baby dies. This may be due to not getting enough oxygen in the uterus, prematurity, or other causes of foetal distress.

What are the risks to others?
Complications may harm the baby or cause its death.

What are the treatments for the condition?
Treatment varies depending on:
  • the amount of bleeding
  • the age of the foetus
  • the well-being of the foetus
  • whether the condition is complete or partial
  • the position of the foetus
  • the mother's well-being
  • whether labour has begun
In asymptomatic or mild cases, bed rest and no sexual intercourse may be advised. As the uterus grows, the placenta may move to a safer position. Other treatment may include:
  • using foetal monitors as needed
  • giving the mother fluids through a vein
  • monitoring the mother's vital signs, such as blood pressure, heart rate, and urine output
  • observing, but not interfering with, the pregnancy if tests and signs suggest mother and foetus are fine
  • giving the mother blood transfusions to replace lost blood if the foetus is immature, not in distress, and younger than 36 weeks old
  • allowing a vaginal birth if the mother and foetus are stable
  • giving the mother a caesarean section if she and the foetus are not stable
Once a foetus is 36 weeks old, a caesarean section is generally done to avoid potential complications for mother and baby. First, though, tests may be done to check foetal maturity.

What are the side effects of the treatments?
The treatments for this condition may be lifesaving. Possible side effects should be weighed against the loss of life. Any surgery can cause bleeding and infection. Blood transfusions and medications can cause allergic reactions.

What happens after treatment for the condition?
After the birth, the woman will be watched closely for signs of continued bleeding through:
  • full blood counts, or FBCs
  • blood tests to monitor the ability of her blood to clot
  • vital signs
If the baby survives, he or she will be monitored in the intensive care unit.

How is the condition monitored?
A woman will be closely monitored throughout pregnancy to determine the status of the foetus, as well as her own health.

Author: Eva Martin, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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