The placenta is an incredible specialist organ that grows in the uterus during pregnancy. Its role is to provide developing babies with everything they need for the duration of the pregnancy.

The placenta is the ‘go between’ between mum and baby. It takes nutrients and oxygen from the maternal blood system, and passes them on to the baby via the placenta and umbilical cord.

Without the placenta, your baby would not be able to survive.

Basically, it has a pretty big job to do.

Where does the placenta form?

The placenta can develop in any area of the uterus. It will develop wherever the fertilized egg implants into the uterine wall.

Depending on its location, the placenta can be described as:

Fundal placenta – at the top of the uterus
Anterior Placenta – on the front side of the uterus, closest to the abdomen
Posterior Placenta – on the back side of the uterus, closest to the back
Lateral placenta – on the right or left side of the uterus.

What is placenta previa?

You might have heard of a placental condition called placenta previa, or perhaps you know someone who’s been diagnosed with it.

What exactly is it, and what does it mean?

Placenta previa – definition

Placenta previa — also spelt placenta praevia — literally means ‘placenta first’.

In early pregnancy, as the placenta develops, instead of attaching in the upper or middle area of the uterine wall, the placenta attaches in the lower section of the uterus.

If the placenta embeds itself too low down in the uterus, it can cover, or partially cover, the cervix; that’s when placenta previa occurs.

The placenta can block your baby’s descent into the birth canal.

Placenta previa types

There are 3 types of placenta previa but you might hear health professionals using the general term placenta previa when referring to any of them.

The 3 types are:

Complete. If the placenta completely covers the cervix, a complete placenta previa is diagnosed
Partial. If the placenta partially covers the cervix, this is known as partial placenta previa
Marginal. If the placenta is near to, but not touching, the cervix, this is known as a marginal placenta previa, or a Low Lying Placenta. A placenta is usually referred to as low lying if the edge of the placenta is within 20mm (2cm) from the cervix.

How common is placenta previa?

Complete placenta previa is a relatively uncommon condition that occurs in around 0.5% of births, or 1 in every 200.

How is placenta previa diagnosed?

Placenta previa is diagnosed by an ultrasound scan.

Most women will choose to have an ultrasound scan in their second trimester, usually around 18-20 weeks of pregnancy.

This scan is sometimes referred to as the anatomy scan, or the anomaly scan.

It’s not just your baby that the sonographer will be checking. The scan will also involve taking a look at where the placenta is positioned, to see whether the placenta covers the cervix.

It’s usually at this scan that placenta previa or a low lying placenta is discovered.

Should I be worried about placenta previa symptoms?

It’s not all doom and gloom if you’re diagnosed with marginal placenta previa or Low Lying Placenta.

If you have a low lying placenta at 18-20 weeks, in most cases it is still very early to predict what could happen.

In your Third Trimester the bottom part of your uterus does most of its growing and stretching and will often take the placenta with it.

It doesn’t ‘migrate’ upwards but because it’s attached to the uterine wall it is carried upwards as the uterus grows.

Placenta previa ultrasound

If you’ve been told you have a marginal or low lying placenta, your doctor will offer you an additional scan between 32 and 36 weeks. The purpose of this scan is to check to see whether your placenta has moved away from the cervix.

An ultrasound late in your third trimester will give you a better picture of what’s really going on.

In the majority of cases, a low lying placenta will resolve itself by the third trimester, so you won’t need to worry about it.

Only a few women will go on to develop a true placenta previa. In just 0.5% of cases (1 in every 200 cases of placenta previa) the placenta not move up out of the way.

In this small percentage of cases, the placenta remains low – either partially or fully covering the cervix – and the pregnant woman will develop a complete or partial placenta previa.

What causes placenta previa?

No-one knows exactly what causes placenta previa; we do know, however, it’s less common in first pregnancies.

Any condition involving scarring of the uterus will increase the chances of placenta previa.

There are certain conditions which make placenta previa more likely to occur:

Past pregnancy. The risk of placenta previa increases with each pregnancy
Multiple pregnancies. If you’re pregnant with twins or triplets, the area in the uterus that’s occupied by the placenta (or placentas) will be larger. This increases the chance of the placenta being close to, or covering, the cervix
Previous cesarean deliveries. Women who have had a previous cesarean delivery are at greater risk of placenta previa, due to scarring of the uterus. The more cesarean deliveries a woman has, the greater her risk of placenta previa
Previous placenta previa. If you’ve had placenta previa diagnosed in a previous pregnancy you’ve a greater chance of developing it again
Past uterine surgeries. Surgeries, including D&C (Dilation And Curettage), procedures following a miscarriage or abortion or surgery to remove fibroids can all cause scarring on the uterus. Scarring increases the chance of the placenta attaching low in the uterus
Uterine fibroids. Fibroids are benign tumours that grow in the uterus. They can become quite large, which limits the space available for the placenta to attach. The placenta is therefore more likely to attach in the lower part of the uterus
IVF (in vitro fertilization). Some studies have recently shown that women who use assisted reproductive technologies (ART) could be at increased risk of placenta previa.

Given the number of cesarean sections and ART procedures is on the increase, this could result in a growing incidence of placenta previa.

The following factors have also been found to increase the risk of placenta previa:

Smoking or using illegal drugs
Becoming pregnant when aged over 35 years.

Placenta previa Symptoms

The biggest symptom of placenta previa is painless vaginal bleeding. Bleeding can occur at any gestational age, but is more common in the later stages of pregnancy.

For more information, read our article Bleeding During Pregnancy – 7 Causes Of Blood Loss.

Bleeding is caused as the uterus thins out towards the end of pregnancy, in preparation for labor. This causes the area of the placenta that covers the cervical opening to bleed as the blood vessels that supply it are disrupted.

This will cause sudden, painless uncontrolled bleeding, usually towards the end of the second trimester to the third trimester.

It will appear as bright red blood, which might be a small amount, or it could be heavy bleeding. The pregnant woman might also experience some cramping.

The bleeding might stop by itself, but women can experience further episodes of bleeding before reaching their estimated due date.

Placenta previa with no bleeding

On the other hand, some women don’t experience any symptoms of placenta previa. They will have no vaginal bleeding at all until they go into labor.

The more the placenta covers the cervix, the earlier the haemorrhage can occur, and the greater the amount of blood lost.

Remember, no amount of blood loss in your second or third trimester is normal –even if it’s only a small amount.

It’s always important to seek medical attention immediately, to prevent other complications.

Given there are several causes of bleeding during pregnancy, this one symptom alone is not enough to diagnose placenta previa accurately; other diagnostic tests, such as ultrasound, will be needed to confirm the condition.

For example, a placental abruption also results in sudden, bright red, heavy blood loss.

Placenta previa – effects on baby

Placenta previa can potentially cause complications for both the mother and her baby.

Placenta previa can cause severe bleeding in the mother, but can also affect the baby’s growth and development in the womb.

Other risks include:

Preterm Birth
Growth restriction
Birth defects
Infection after the birth.

The main reason for infant deaths in cases of placenta previa is premature birth, where the baby has been born before 36 weeks of pregnancy.

How is placenta previa treated?

If you have placenta previa, it’s likely you’ll need to birth your baby by cesarean section, depending on the grade of placenta previa. Previas are graded 1-4, with 4 being the most serious.

You might be able to birth vaginally if you have a grade 1 or 2 placenta previa (minor); if you have grades 3 or 4 (major), however, a cesarean section will be necessary to prevent severe bleeding and the need for a blood transfusion.

If you don’t go into labor beforehand, your cesarean will probably be booked in at about 38 weeks, when your baby is more mature. If you go into labor earlier than this, you’ll need an emergency c-section.

The most serious placenta previa cases will often involve being admitted for a hospital stay. Early delivery might also be required in the case of serious bleeding, and blood transfusions might also be necessary.

How to plan for an unplanned cesarean

Some women find the thought of a c-section upsetting. Being unable to have a vaginal delivery can leave some women feeling as though the birth will be a failure on their part.

However, birthing your baby by c-section is not a failure. For some women, it’s the safest way – and sometimes the only way – to bring their babies into the world.

If you have trouble dealing with your emotions, it’s important to seek the help of an experienced perinatal psychologist, who specializes in pre and postnatal issues.

To help with c-section healing, it can also be helpful to join a support group. See the Birthrites and Birthtalk websites for more information.

What can I do if I am diagnosed with placenta previa?

Unfortunately, there’s nothing you can do to change the position of the placenta. Therefore, there is little you can do to help the situation.

Increase your Iron Intake During Pregnancy, in order to prevent anaemia. Keeping your iron levels topped up during pregnancy is important, due to the increased chance of severe blood loss.

An effective, quality iron supplement is essential for keeping your iron stores topped up.

During pregnancy, however, you are more prone to constipation, and some iron supplements might increase your chances of getting constipated.

Speak to your naturopath for an effective, but gentle brand.

Placenta previa do’s and dont’s

If you have experienced vaginal bleeding, you might be required to take bed rest – either at home or in hospital – and refrain from sexual intercourse, depending on your situation.

Other things to consider:

Examinations. If you have placenta previa, or your placenta is near the cervix, avoid transvaginal ultrasound and internal vaginal examinations
Awareness. Make sure anyone looking after you is aware that you are at increased risk of bleeding
Seeking help. If you have any episodes of bleeding, do not ignore them
Only use pads (not tampons) if you are bleeding
Avoid heavy lifting.

Further reading: Placenta Previa | What You Need To Know.