This is a condition when part or the whole of the placenta is lying across the cervix instead of being attached higher up on the mother’s uterine wall. In placenta praevia, the placenta is quite literally “in front of” the baby’s head. This means the placenta is blocking the baby’s exit out of the mother’s womb, creating a barrier which the baby cannot get past. Placenta praevia occurs once in around every 200 pregnancies.
The first sign that a mother may have placenta praevia is when she has a painless vaginal bleed, most commonly around 30 weeks of her pregnancy, though it sometimes occurs earlier. Often placenta praevia is diagnosed during an ultrasound, even before a mother has any symptoms herself.
Although it is common in early pregnancy for the placenta to attach itself fairly low in the womb, as the pregnancy progresses and the womb expands the placenta tends to move upwards. Generally, even when a mother has been diagnosed as having placenta praevia, there are no issues until the third trimester.
The lower part of the womb thins out and stretches to accommodate the growing baby. But as this stretching and thinning occurs, it can shear a part of the placenta away. This is why it can sometimes be hard to determine if a mother has a placenta praevia or the placenta has actually abrupted away from the uterine wall.
Is it always severe?
Placenta praevia is assessed as being either partial or complete. If it is partial, with only the lower edge covering the cervix, then there is sometimes still room for the baby’s head to pass through. This means that a vaginal delivery is still possible. However, if the placenta is covering the entire cervix, caesarean section delivery of the baby is the only option.
When a major or complete placenta praevia occurs, there is a significant chance of the mother having a large bleed either before or after she goes into labour. Essentially, the closer a placenta lies to the mother’s cervix, the more chance she has of bleeding. The placenta is a huge organ, well supplied with blood and large vessels. Unless it is firmly attached to the uterine wall and the blood transfer sealed, there is inevitably a loss of blood around the areas that are not well connected.
Why does it happen?
The exact reason is unclear. Very early on in the pregnancy the placenta attaches to the womb in order to supply the baby with oxygen and nutrients. In the majority of women, the placenta secures itself where it needs to and there are no problems. Placenta praevia is more likely in:
- Women who have had previous pregnancies
- Women who have had uterine surgery, for example a curette or a previous caesarean section delivery
- Older women
- Multiple pregnancies where there is more crowding in the womb
- Women who smoke cigarettes
- Women that have abnormalities in the placenta itself
How will I know if I have Placenta Praevia?
You won’t know unless you are told you do when you have a pregnancy ultrasound. One of the goals of gestational ultrasound is to identify the position and size of the placenta. You may be told you have a low lying placenta or a praevia in which case you will be monitored closely. Regular ultrasounds are often recommended to assess if the placenta is moving upwards as the womb expands. Signs of placenta praevia include:
- Bright red blood loss from the vagina. This is usually painless and looks very fresh.
- Presenting as a breech (bottom first instead of the head) or transverse (lying across the womb). This is because the space in the womb where the baby would normally lie is being taken up by the placenta. When your midwife or obstetrician examines your abdomen they will note the position of the baby.
If you have had placenta praevia previously you should be extra alert.
What are the Risks of Placenta Praevia?
To the Mother:
- Excessive bleeding, which is difficult to control
- A change in her plans for delivery preference, i.e. a caesarean section becomes the only option
- Premature birth and its associated risks
- In extreme cases, hysterectomy may become necessary if the placenta does not separate from the lining of the womb
- Shock from blood loss
To the Baby:
- Premature delivery and its associated risks
- Loss of adequate oxygen with potential brain injury and death
- Blood loss and resultant anaemia for the baby
What’s the Treatment?
There is no specific treatment other than watching and waiting. If a mother does not have a bleed then there is no special management. If she does, then bed rest and close monitoring is necessary. The general recommendation is to abstain from sex during episodes of bleeding. Any trauma to the cervix is best avoided. Similarly, any activity that could initiate uterine contractions, such as nipple stimulation or orgasm, is not recommended.
Is it Still Possible to have a Normal Delivery?
Some mothers will have very minor bleeding, or no bleeding at all even though they do have placenta praevia. However, a caesarean section delivery may still be necessary. The placenta can become dislodged or stop the baby’s head and body from descending in the womb. This can potentially cause problems with obstructing labour or failure of the labour to progress.
In cases where bleeding is significant:
- The mother will need to be hospitalised for close observation
- A mother may require a blood transfusion to boost her own circulating blood volume
- She may need to have investigations into her blood composition to ensure she does not have any problems with her blood clotting times
- She may need to have an injection of Anti-D if she has a negative blood group
- The baby will need to be monitored by the use of a scalp electrode during labour or a cardiotocograph
Treatment options are designed to maximise the amount of time the baby has in the womb, while not compromising the mother or baby’s safety. Generally, caesarean section delivery is booked for 37 weeks of gestation when a mother has placenta praevia. This means the baby will be mature enough to breathe independently, though not be so premature they will face health issues.