The placenta develops at the same time as your baby and is attached to the lining of your uterus (womb) during pregnancy. It allows for oxygen and nutrients to pass from you to your baby as well as producing hormones that support your pregnancy.
The fertilised ovum (egg) implants into the lining of your uterus and the placenta grows from there. As your pregnancy progresses and your baby and placenta increase in size, your womb expands and this affects the placenta’s position. The area where the placenta is usually attached stretches upwards, moving the placenta away from your cervix.
If the placenta stays low in your womb, near to or covering your cervix, it may block the baby’s way out. This is called ‘low-lying placenta’ or ‘placenta praevia’.
The position of your placenta will be recorded at your 18-22 week ultrasound scan. If your placenta is significantly low, you’ll be offered an extra ultrasound scan later in your pregnancy (usually at about 32 weeks) to check its position again. For most women, the placenta will have moved into the upper part of the womb by this stage
What causes placenta praevia?
There is no obvious cause for placenta praevia. It may be that there is a larger placenta area (such as, if you are having twins) or there could be scar tissue from a previous caesarean or curette. There are several factors that can increase your risk of placenta praevia, including having had a caesarean section in the past (especially if your last baby was born by caesarean), and older age in the mother.
Placenta praevia symptoms
Signs that the placenta could be low-lying include painless, bright red bleeding from the vagina (either spontaneously or after sex) any time after 20 weeks of pregnancy. Placenta praevia is the most common cause of painless bleeding in the last trimester of pregnancy.
You may also experience:
- Cramping in your uterus with bleeding
- Bleeding during labour
If you experience bleeding during your pregnancy, contact your midwife or doctor immediately.
Types of placenta previa
Type 1: Low-lying placenta previa
Only small part of placenta encroaches towards the lower segment but doesn’t reach the internal os.
Type 2: Marginal placenta previa
The placenta does not cover internal os but reaches the margin of it.
Type 3: Incomplete or partial central placenta previa
The placenta covers the internal os partially.
Type 4: Central or complete placenta previa
The placntacompletely overs the internal os even after os is fully dilated.
Placenta praevia treatment
Placenta praevia is graded into 4 categories from minor to major. If you have grade 1 or 2 it may still be possible to have a vaginal birth, but grade 3 or 4 will require a caesarean section.
Any grade of placenta praevia will require you to live near or have easy access to the hospital in case you start bleeding. Heavy bleeding may mean you need to be admitted to hospital for the remainder of your pregnancy.
When you are in hospital, your blood will be taken to make sure an exact donor blood match is available in case you need a blood transfusion.
You may also need to take iron tablets if you have anaemia (low blood haemoglobin level). If you have bleeding during your pregnancy and have Rh negative blood, you will need an injection of Anti D so your baby is not affected by the bleeding.