Low Lying Placenta (Placenta Previa) – What does it mean?

A low lying placenta occurs when the fertilised egg attaches itself to the lower part of the uterus. Often with a low lying placenta, as the uterus grows the placenta is pulled further up the uterus, but in a small number of pregnancies it remains low.

For a natural delivery to occur the placenta needs to be at least 2cm away from the opening of the cervix. A low lying placenta means that there is a risk that the placenta maybe too close to the cervix or that it may cover the entrance all together. If, at the time of birth, the placenta is considered to be too low for a natural birth to occur, it is known as placenta praevia. Only between two and five percent of low lying placentas will become placenta praevia.

Low lying placenta is usually diagnosed at the 20 week scan. If this is the case, another scan is offered between 32 and 34 weeks (depending on how low the placenta is). This scan is to determine if the placenta has moved up and away from the entrance to the cervix.

In most cases, the placenta moves up and a natural delivery is possible. However, in a small number (around one in 200 pregnancies) the placenta remains too low for a vaginal birth. If placenta praevia is diagnosed the baby will be born via caesarean section.

There is no specific cause of placenta preavia, but women are at higher risk of this condition if:

• there is a very large placenta (for example, with twins)
• there is scarring on the lining of the uterus either from a previous caesarean or D&C
• late implantation of the fertilised egg
• the mother is a smoker.

However, a low lying placenta can also occur in women that have none of the risk factors. Unfortunately, there is nothing that can be done to fix or move the placenta, and it is more a case of ensuring a timely and correct diagnoses and planning a caesarean birth for the safe delivery of the baby.

Early in the pregnancy there are often no symptoms of a low lying placenta, which is why it is most commonly diagnosed at the 20 weeks scan.

If it is missed at the 20 weeks scan, symptoms in the latter part of the pregnancy that may indicate placenta praevia are:

• sudden bright red, painless bleeding
• painless bleeding after sex
• bleeding during labour
• uterine cramping and bleeding.

Symptoms are more likely to occur in the latter part of the pregnancy as the placenta stretches as the lower part of the uterus grows and thins out to accommodate the growing baby. This growth can result in the placenta stretching and tearing, causing the placenta to bleed. Any vaginal bleeding in pregnancy should be checked by your doctor.

Depending on the severity of the placenta praevia and the extent of any bleeding, you may be able to remain at home; however, you will need to be close to the hospital in case you experience further bleeding. In most cases doctors will recommend bed rest and abstaining from sex.

Placenta praevia can be managed by your doctor with little or no consequences; however, if intervention is not sought it can be fatal. Although this is rare, it is important to keep all your medical appointments and follow your doctor’s advice.