The cause of pre-eclampsia is not fully understood. However, it is thought that the placenta does not develop properly because of a problem with the blood vessels supplying it.

Placenta

The placenta is the organ that links the mother’s blood supply to her unborn baby’s blood supply. Food and oxygen pass through the placenta from mother to baby. Waste products can pass from the baby back into the mother.

To support the growing baby, the placenta needs a large and constant supply of blood from the mother. In pre-eclampsia, the placenta does not get enough blood. This could be because the placenta did not develop properly as it was forming during the first half of the pregnancy.

The problem with the placenta means that the blood supply between mother and baby is disrupted. Signals from the damaged placenta affect the mother’s blood vessels, causing high blood pressure (hypertension)

At the same time, problems in the kidneys may cause valuable proteins that should remain in the mother’s blood to leak into her urine, resulting in protein in the urine (proteinuria).

What causes problems with the placenta?

In the initial stages of pregnancy, the fertilised egg implants itself into the wall of the womb (uterus). The womb is a hollow organ a baby grows inside during pregnancy. The fertilised egg produces root-like growths called villi, which help to anchor it to the lining of the womb.

The villi are fed nutrients through blood vessels in the womb and will eventually grow into the placenta. During the early stages of pregnancy, these blood vessels change shape and become wider.

If the blood vessels do not fully transform, it is likely that the placenta will not develop properly because it will not get enough nutrients. This may then lead to pre-eclampsia.

It is still unclear why the blood vessels do not transform as they should. It is likely that inherited changes in your genes have some sort of role, as the condition often runs in families.

Who is most at risk?

Some factors have been identified that could increase your chances of developing pre-eclampsia. These are listed below.

• it is your first pregnancy – pre-eclampsia is more likely to happen during the first pregnancy than during any subsequent pregnancies
• it has been at least 10 years since your last pregnancy
• you have a family history of the condition – for example, your mother or sister has had pre-eclampsia
• you previously had pre-eclampsia – there is an approximately 16% chance that you will develop the condition again in later pregnancies
• you are over the age of 40
• you have an existing medical problem – for example, diabetes, kidney disease or high blood pressure
• you were obese at the start of your pregnancy (you had a body mass index of 30 or more)
• you are expecting multiple babies, such as twins or triplets

If you are considered to be at a high risk of developing pre-eclampsia, you may be advised to take a 75mg dose of aspirin (baby aspirin or low-dose aspirin) every day during your pregnancy from when you are 12 weeks pregnant until your baby is born. Evidence suggests this can help lower your chances of developing the condition.

Although they are rare, a number of complications can develop if pre-eclampsia is not diagnosed and monitored.

These can affect both the mother and her baby.

Problems affecting the mother

Fits (eclampsia)

Eclampsia is a term that describes a type of convulsion or fit (involuntary contraction of the muscles) that pregnant women can experience, usually from week 20 of the pregnancy or immediately after the birth. Eclampsia is quite rare in the UK, with an estimated 1 case for every 4,000 pregnancies.

During an eclamptic fit, the mother’s arms, legs, neck or jaw will twitch involuntarily in repetitive, jerky movements. She may lose consciousness and may wet herself. The fits usually last less than a minute.

While most women make a full recovery after having eclampsia, there is a small risk of permanent disability or brain damage if the fits are severe. Of those who have eclampsia, around 1 in 50 will die from the condition. Unborn babies can suffocate during a seizure and 1 in 14 may die.

Research has found that a medication called magnesium sulfate can halve the risk of eclampsia and reduce the risk of the mother dying. It is now widely used to treat eclampsia after it has occurred, and to treat women who may be at risk of developing it.

HELLP syndrome

HELLP syndrome is a rare liver and blood clotting disorder that can affect pregnant women. It is most likely to occur immediately after the baby is delivered, but can appear any time after 20 weeks of pregnancy, and in rare cases before 20 weeks.

The letters in the name HELLP stand for each part of the condition:

• ‘H’ is for haemolysis – this is where the red blood cells in the blood break down
• ‘EL’ is for elevated liver enzymes (proteins) – a high number of enzymes in the liver is a sign of liver damage
• ‘LP’ is for low platelet count – platelets are cells in the blood that help it to clot

HELLP syndrome is potentially as dangerous as eclampsia, and is slightly more common. The only way to treat the condition is to deliver the baby as soon as possible. Once the mother is in hospital and receiving treatment, it is possible for her to make a full recovery. 

Stroke

The blood supply to the brain can be disturbed as a result of high blood pressure. This is known as a cerebral haemorrhage, or stroke. If the brain does not get enough oxygen and nutrients from the blood, brain cells will start to die, causing brain damage and possibly death.

Organ problems

• pulmonary oedema – where fluid builds up in and around the lungs. This stops the lungs from working properly by preventing them from absorbing oxygen.
• kidney failure – when the kidneys cannot filter waste products from the blood. This causes toxins and fluids to build up in the body.
• liver failure – disruption to the functions of the liver. The liver has many functions, including digesting proteins and fats, producing bile and removing toxins. Any damage that disrupts these functions could be fatal.

Blood clotting disorder

The mother’s blood clotting system can break down. This is known medically as disseminated intravascular coagulation.

This can either result in too much bleeding because there aren’t enough proteins in the blood to make it clot, or in blood clots developing throughout the body because the proteins that control blood clotting become abnormally active.

These blood clots can reduce or block blood flow through the blood vessels and possibly damage the organs.

Problems affecting the baby

Babies of women with pre-eclampsia tend to develop more slowly in the womb than normal because the condition reduces the amount of nutrients and oxygen passed from the mother to her baby. This means that these babies are often smaller than usual, particularly if the pre-eclampsia occurs before 37 weeks.

If pre-eclampsia is severe, a baby may need to be delivered before they are fully developed. This can lead to serious complications, such as breathing difficulties caused by the lungs not being fully developed (neonatal respiratory distress syndrome). In these cases, a baby will usually need to stay in a neonatal intensive care unit so they can be monitored and treated.

Some babies of women with pre-eclampsia can even die in the womb and be stillborn. It’s estimated that around 1,000 babies die each year because of pre-eclampsia. Most of these babies die because of complications related to early delivery.

Although you will not usually notice the early signs of pre-eclampsia, the condition can easily be diagnosed during the routine checks you have while you’re pregnant.

During these antenatal appointments, your blood pressure is regularly checked for signs of high blood pressure and a urine sample is tested to see if it contains protein.

If you notice any of the symptoms of pre-eclampsia between your antenatal appointments, see your midwife or GP for advice.

Blood pressure

Blood pressure is a measure of the force of the blood on the walls of the arteries (main blood vessels) as the blood flows through them. It is measured in millimetres of mercury (mmHg) and recorded as two figures:

• systolic pressure – the pressure when the heart beats and squeezes blood out
• diastolic pressure – the pressure when the heart rests inbetween beats

Your GP or midwife will use a device with an inflatable cuff and a scale as a pressure gauge (a sphygmomanometer) to measure your blood pressure. The systolic reading will be taken first, followed by the diastolic reading.

If, for example, the systolic blood pressure is 120mmHg and the diastolic blood pressure is 80mmHg, the overall blood pressure will be 120 over 80, which is commonly written as 120/80.

High blood pressure during pregnancy is usually defined as a systolic reading of 140mmHg or more, or a diastolic reading of 90mmHg or more.

Urine tests

A urine sample is usually requested at every antenatal appointment. This can easily be tested for protein using a dipstick. A dipstick is a strip of paper that has been treated with chemicals so it reacts to protein, usually by changing colour.

If the dipstick is positive for protein, your GP or midwife may ask for another urine sample to send to a laboratory for further tests. This could be a single sample of urine, or you may be asked to provide several samples of urine over a 24-hour period. These can be used to determine exactly how much protein is being lost through your urine.

Further tests in hospital

If you are diagnosed with pre-eclampsia, you should be referred to a specialist working in a hospital for further tests and more frequent monitoring.

Depending on the severity of your condition, you may be able to go home after an initial assessment and have frequent outpatient appointments. In severe cases, you may need to stay in hospital for closer observation.

Read more information about treating pre-eclampsia.

Pre-eclampsia is a condition that affects some pregnant women, usually during the second half of pregnancy (from around 20 weeks) or soon after their baby is delivered.

Early signs of pre-eclampsia include having high blood pressure (hypertension) and protein in your urine (proteinuria). It is unlikely you will notice these signs, but they should be picked up during your routine antenatal appointments.

In some cases, further symptoms can develop, including:

• swelling of the feet, ankles, face and hands caused by fluid retention (oedema)
• severe headache
• vision problems
• pain just below the ribs

If you notice any symptoms of pre-eclampsia, seek medical advice immediately by calling your midwife, GP surgery or NHS 111.

Although many cases are mild, the condition can lead to serious complications for both mother and baby if it is not monitored and treated (see below). The earlier pre-eclampsia is diagnosed and monitored, the better the outlook for mother and baby.

Read more about the symptoms of pre-eclampsia and diagnosing pre-eclampsia.

Who is affected?

Pre-eclampsia affects up to 5% of pregnancies, and severe cases develop in about 1-2% of pregnancies.

There are a number of things that can increase your chances of developing pre-eclampsia, such as:

• if it is your first pregnancy
• if you developed the condition during a previous pregnancy
• if you have a family history of the condition
• if you are over 40 years old
• if you are expecting multiple babies (twins or triplets)

If you are thought to be at a high risk of developing pre-eclampsia, you may be advised to take a daily dose of low-dose aspirin from the 12th week of pregnancy until your baby is delivered.

What causes pre-eclampsia?

Although the exact cause of pre-eclampsia is not known, it is thought to occur when there is a problem with the placenta (the organ that links the baby’s blood supply to the mother’s).

Read more about the causes of pre-eclampsia.

Treating pre-eclampsia

If you are diagnosed with pre-eclampsia, you should be referred for an assessment by a specialist. This will usually be in a hospital.

While in hospital you will be monitored closely to determine how severe the condition is and whether a hospital stay is needed.

The only way to cure pre-eclampsia is to deliver the baby, so you will usually be monitored regularly until it is possible for your baby to be delivered. This will normally be at around 37-38 weeks of pregnancy, but it may be earlier in more severe cases.

At this point, labour may be started artificially (induced) or you may have a caesarean section (delivery through an incision in the stomach).

Medication may be recommended to lower your blood pressure while you wait for your baby to be delivered.

Read more about treating pre-eclampsia.

Complications

Although most cases of pre-eclampsia cause no problems and improve soon after the baby is delivered, there is a risk of serious complications that can affect both the mother and her baby.

There is a risk the mother will develop fits called eclampsia. These fits can be life threatening for the mother and the baby, but they are rare.

Overall, complications of pre-eclampsia are responsible for the deaths of around six or seven women every year in the UK. About 1,000 babies die each year in the UK because of the condition, mostly because of complications of early delivery, such as severe breathing difficulties.

Read more about the complications of pre-eclampsia.

Pre-eclampsia rarely happens before the 20th week of pregnancy. Most cases occur in the third trimester, after 24-26 weeks.

Although less common, the condition can also develop for the first time during the first six weeks after the birth.

Generally, the earlier pre-eclampsia develops the more severe the condition will be.

Early symptoms

Initially, pre-eclampsia causes:

• high blood pressure (hypertension)
• protein in urine (proteinuria)

You probably won’t notice these symptoms, but your GP or midwife should pick them up during your routine antenatal appointments.

High blood pressure affects 10-15% of all pregnant women, so this alone does not suggest pre-eclampsia. However, if protein in the urine is found at the same time as high blood pressure, it is a good indicator of the condition.

Read more about diagnosing pre-eclampsia.

Further symptoms

As pre-eclampsia develops, it can cause fluid retention (oedema), which often leads to the sudden swelling of the feet, ankles, face and hands.

Oedema is another common symptom of pregnancy, but it tends to be in the lower parts of the body, such as the feet and ankles. It will gradually build up during the day. If the swelling is sudden and it particularly affects the face and hands, it could be pre-eclampsia.

As pre-eclampsia progresses, it may cause:

• severe headaches
• vision problems, such as blurring or seeing flashing lights
• pain just below the ribs
• vomiting
• excessive weight gain caused by fluid retention
• feeling very unwell

If you notice any symptoms of pre-eclampsia, seek medical advice immediately by calling your GP surgery or NHS 111.

Without immediate treatment, pre-eclampsia may lead to a number of serious complications, including:

• convulsions (eclampsia)
• HELLP syndrome, a combined liver and blood clotting disorder
• stroke

However, these complications are rare. Read more about the complications of pre-eclampsia.

Signs in the unborn baby

The main sign of pre-eclampsia in the unborn baby is slow growth. This is caused by poor blood supply through the placenta to the baby.

The growing baby receives less oxygen and fewer nutrients than it should, which can affect development. This is called intra-uterine or foetal growth restriction.

If your baby is growing more slowly than usual, this will normally be picked up during your antenatal appointments.

Pre-eclampsia can only be cured by delivering the baby. If you have pre-eclampsia, you will be closely monitored until it is possible to deliver the baby.

Once diagnosed, you will be referred to a hospital specialist for further assessment and any necessary treatment.

If you only have high blood pressure without any signs of pre-eclampsia, you can usually return home afterwards and will attend regular (possibly daily) follow-up appointments.

If pre-eclampsia is confirmed, you will usually need to stay in hospital until your baby can be delivered.

Monitoring in hospital

While you are in hospital, you and your baby will be monitored in the following ways:

• your blood pressure will be checked regularly for any abnormal increases
• urine samples may be taken regularly to measure protein levels
• your blood may be tested for the proteins aspartate aminotransferase (AST) or alanine aminotransferase (ALT), which can be a sign of liver damage if found in the blood
• a blood test may be taken to provide information about the blood cells
• you may have ultrasound scans to check blood flow through the placenta, measure the growth of the baby, and observe the baby’s breathing and movements
• the baby’s heart rate may be monitored electronically in a process called cardiotocography, which can detect any distress in the baby

Medication for high blood pressure

Medication is recommended to help lower your blood pressure. These medications will reduce the likelihood of serious complications, such as stroke. Some of the medications used regularly in the UK include labetalol, nifedipine or methyldopa.

Of these medications, only labetalol is specifically licensed for use in pregnant women with high blood pressure. This means the medication has undergone clinical trials that have found it to be safe and effective for this use.

However, while methyldopa and nifedipine are not licensed for use in pregnancy, they can be used ‘off-label’ (outside their licence) if it is felt that the benefits of treatment are likely to outweigh the risks of harm to you or your baby.

These medications have been used by doctors in the UK for many years to treat pregnant women with high blood pressure and they are recommended as possible alternatives to labetalol in guidelines produced by the National Institute for Health and Care Excellence (NICE). Therefore, your doctors may recommend one of them if they think it is the most suitable medication for you. 

If your doctors recommend treatment with one of these medications, you should be made aware that the medication is unlicensed in pregnancy and any risks should be explained before you agree to treatment, unless immediate treatment is needed in an emergency.

Other medications

Anticonvulsant medication may be prescribed to prevent fits if you have severe pre-eclampsia and your baby is due within 24 hours, or if you have had convulsions (fits). They can also be used to treat fits if they occur.

Delivering your baby

In most cases of pre-eclampsia, having your baby at about the 37th to 38th week of pregnancy is recommended. This may mean labour needs to be started artificially (induced labour) or you may need to have a caesarean section (delivery through an incision in the stomach).

This is recommended because research suggests there is no benefit in waiting for labour to start by itself after this point. Delivering the baby early can also reduce the risk of complications from pre-eclampsia.

If your condition becomes more severe before 37 weeks and there are serious concerns about the health of you or your baby, earlier delivery may be necessary. Deliveries before 37 weeks are known as premature births and babies born before this point may not be fully developed.

You should be given information about the risks of both premature birth and pre-eclampsia so that the best decision can be made about your treatment.

After the delivery

Although pre-eclampsia will usually improve soon after your baby is born, complications can sometimes develop a few days later. You may therefore need to stay in hospital after the delivery so you can be monitored.

Your baby may also need to be monitored and may need to stay in a hospital neonatal intensive care unit if born prematurely. These units have facilities that can replicate the functions of the womb and allow your baby to develop fully. Once it is safe to do so, you will be able to take your baby home.

You will usually need to have your blood pressure checked regularly after leaving hospital, and you may need to continue taking medication to lower your blood pressure for several weeks.

You should be offered a postnatal appointment six to eight weeks after your baby is born to check your progress and decide if any treatment needs to continue.