Low-lying placenta (placenta praevia): Causes, symptoms, diagnosis, treatment
What is placenta praevia or low-lying placenta?
Low-lying placenta, or placenta praevia, is a complication of pregnancy where the placenta that feeds the growing baby is attached to the lower part of the womb near to or covering the cervix.
Low-lying placenta may be picked up during a routine 20-week ultrasound scan appointment.
In some cases, a placenta that is seen to be low-lying will move upwards later in pregnancy.
Any bleeding from placenta praevia at the entrance to the womb in the second half of the pregnancy can be heavy and a risk to the baby and the mother's health. After a low-lying placenta diagnosis, seek medical advice if there's any bleeding during pregnancy.
Having a low-lying placenta means it is more likely a caesarean section delivery will be recommended.
There are several types of placenta praevia:
- A low-lying placenta is near the cervical opening but not covering it. It will often move upward in the uterus as your due date approaches.
- A partial placenta praevia covers part of the cervical opening.
- A total placenta praevia covers and blocks the cervical opening.
What causes a placenta praevia?
The cause of placenta praevia is usually unknown, although it occurs more commonly among women who are older, smoke, have had children before, have had a caesarean section or other surgery on the uterus, or have scars inside the uterus.
Women with placenta praevia - specifically if they have a placenta praevia after having delivered a previous baby by caesarean section - are at increased risk of placenta accreta, placenta increta or placenta percreta.
In placenta accreta, the placenta is firmly attached to the uterus. In placenta increta, the placenta has grown into the uterus; and in placenta percreta, it has grown through the uterus. This condition is often first suspected because the woman has both a praevia and a prior caesarean section. It can be confirmed by ultrasound, CT scan or MRI, though those tests are not completely reliable. Women with one of these conditions usually require a hysterectomy after delivery of the baby, because the placenta does not separate from the uterus.
What are the symptoms of placenta praevia?
The main symptom of placenta praevia, and the greatest risk to you and your baby, is vaginal bleeding. If you have bled too much, other symptoms include anaemia, pale skin, rapid and weak pulse, shortness of breath, or low blood pressure. The bleeding that signals placenta praevia may occur at the end of the second trimester or beginning of the third trimester. It may be heavy or light.
Bleeding is usually painless, and it may happen without labour or during labour. Mothers with a placenta praevia are also at increased risk of delivering prematurely, before 37 weeks of pregnancy.