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Pre-eclampsia is a condition that affects some pregnant women during the second half of pregnancy (from around week 20) or immediately after delivery of their baby.

Women with pre-eclampsia have high blood pressure, fluid retention (oedema) and protein in the urine (proteinuria). If it's not treated, it can lead to serious complications.

In the unborn baby, pre-eclampsia can cause growth problems.

Read more about the symptoms of 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).

Pregnant women with pre-eclampsia may not realise they have it. Pre-eclampsia is usually diagnosed during routine antenatal appointments.

Mild pre-eclampsia can be monitored with blood pressure and urine tests at regular antenatal appointments and usually disappears soon after the birth. Severe pre-eclampsia may need to be monitored in hospital.

Who is affected

Mild pre-eclampsia affects up to 10% of first-time pregnancies. More severe pre-eclampsia affects 1-2% of pregnancies. If you have pre-eclampsia during your first pregnancy, you will be more likely to have it again in subsequent pregnancies.

Treating pre-eclampsia

Treatment for pre-eclampsia focuses on lowering blood pressure and managing the other symptoms, sometimes with medication.

The only way to cure pre-eclampsia is to deliver the baby. In some cases this may mean inducing labour (starting labour artificially), although this depends on how far along the pregnancy is. Being born prematurely (before the 37th week of pregnancy) can be dangerous for the baby, but delivery may sometimes be necessary to relieve the mother's symptoms.

Although it is not possible to predict and prevent pre-eclampsia, there is some evidence to show that taking aspirin and calcium supplements early in pregnancy may help. However, you should not take any medication during pregnancy without discussing it with your GP or midwife first.


In some cases further complications can develop, such as eclampsia. This is a type of seizure that can be life-threatening for the mother and the baby. However, this is rare and less than 1% of women with pre-eclampsia develop eclampsia.

Complications of pre-eclampsia are responsible for the deaths of around six women every year in the UK. Several hundred babies also die each year following complications from severe pre-eclampsia, often as a result of premature birth. Therefore, the earlier that pre-eclampsia is diagnosed and monitored, the better the outlook for mother and baby.

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Pre-eclampsia cannot happen until at least the 20th week of pregnancy. Most cases occur in the third trimester (from week 27 to the birth of the baby).

Early symptoms

Pregnant women with pre-eclampsia develop the following symptoms first:

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

High blood pressure affects 10-15% of all pregnant women, so this alone does not suggest pre-eclampsia. However, the presence of protein in the urine is a good indicator of the condition.

Progressive symptoms

As pre-eclampsia develops, it can cause fluid retention (oedema), which often causes 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 in the upper abdomen (just below the ribs)
  • vomiting
  • excessive weight gain due to fluid retention
  • feeling generally unwell

If you notice any symptoms of pre-eclampsia, seek medical advice immediately by calling your GP surgery or NHS Direct Wales on 0845 4647.

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

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

However, these complications are rare.

Read more about the complications of pre-eclampsia.

Symptoms 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 growth restriction, or intra-uterine growth retardation.

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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.


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 (see below).

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) and affecting her kidney function.

Waste products that should be removed from the mother’s blood and passed out in her urine remain in her blood. At the same time, valuable proteins that should remain in her blood are leaked into her urine, causing proteinuria (protein in the urine).

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, pear-shaped organ in which a baby grows during pregnancy. The 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 arteries change shape and become wider. If the arteries 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. Some research has suggested a possible link between pre-eclampsia, miscarriage and infertility. It is possible that the same medical reasons that cause infertility and miscarriage are responsible for the problems that lead to pre-eclampsia.

However, the exact nature of pre-eclampsia and why it affects certain people is still being researched.

Who is most at risk?

Some factors have been identified that could increase your chance 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 had pre-eclampsia in a previous pregnancy. There is an approximately 20% chance that you will develop the condition again in later pregnancies.
  • You are a teenager or are over 40.
  • You have an existing medical problem, for example, diabetes, kidney diseasemigraines 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 (this places more strain on the placenta).
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Pre-eclampsia is diagnosed if both high blood pressure and protein in the urine are discovered by a GP or midwife during a routine antenatal appointment.

Many pregnant women with pre-eclampsia will not notice they have it. Only the GP or midwife will pick it up. However, if you notice any of the symptoms, see your GP.

Blood pressure

Blood pressure is monitored throughout your pregnancy at regular antenatal screenings.

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, which is the pressure when the heart beats and squeezes blood out
  • diastolic pressure, which is the pressure when the heart rests in between beats

Your GP or midwife will use a sphygmomanometer to measure blood pressure (a device with an inflatable cuff and a scale of mercury as a pressure gauge). 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, 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. Severe hypertension is a systolic reading of 160mmHg or more, or a diastolic reading of 110mmHg or more.

Urine tests

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

You will need more frequent antenatal appointments if you have either high blood pressure or protein in your urine. If symptoms are severe or get worse, you may be admitted to hospital for closer observation. Read more information about treating pre-eclampsia.

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Pre-eclampsia can only be cured by delivering the baby. The mother is closely monitored and her blood pressure managed until delivery of the baby is possible.

If you have been diagnosed with pre-eclampsia, you will be referred for further tests. Depending on how severe your symptoms are, this could be another appointment with the GP or midwife in a week’s time, a referral to a hospital within 48 hours or a referral to a hospital on the same day.

Further tests will determine the severity of the pre-eclampsia and whether a hospital stay is necessary.

Mild pre-eclampsia

Mild pre-eclampsia is monitored with frequent antenatal appointments. At these appointments:

  • your blood pressure will be checked for any increase (hypertension)
  • your urine will be tested for protein (proteinuria)
  • you will be asked about any other symptoms you have 

Depending on your symptoms and situation, you will be asked to attend an antenatal appointment at least every three weeks if you are 24-32 weeks into your pregnancy. After 32 weeks of pregnancy, these appointments will be every two weeks.

The National Institute for Health and Clinical Excellence (NICE) and the Pre-eclampsia Community Guideline (PRECOG) have developed recommendations for healthcare professionals to use when treating pre-eclampsia. These include:

  • giving the mother information about the condition based on current evidence, including the signs and symptoms of pre-eclampsia, how it may develop and how serious her case is
  • providing support to enable the mother to make informed decisions about her care
  • arranging a medical review with the mother after any abnormal blood tests, so she can discuss the results and be given a summary of the assessment
  • arranging a new antenatal care plan with the mother, including a follow-up appointment
  • allocating a consultant (a specialist doctor) to the mother
  • providing a way for the mother to report and act on any new symptoms – for example, a direct number to call
  • arranging a convenient way to inform the mother of any future test results

Severe pre-eclampsia

If pre-eclampsia is severe, you may need to be admitted to hospital for closer monitoring and treatment. As pre-eclampsia tends to get worse rather than better, it is unlikely you will be able to go home until after the baby is born.


You and your unborn baby will be monitored in the following ways:

  • your blood pressure will be checked every four to six hours for any abnormal increases
  • urine samples will be taken at least every 24 hours to measure protein levels
  • you will be asked about any other symptoms you are having
  • your blood may be tested for the proteins aspartate aminotransferase (AST) and 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, which create an image of the baby to check blood flow through the placenta, measure the size of the baby and observe the baby’s breathing and movements
  • the baby's growth rate will be closely monitored to check for slow growth
  • the baby's heart rate may be monitored electronically in a process called cardiotocography, which can detect any distress in the baby


Bed rest and medication such as calcium channel blockers can be used to lower blood pressure. This will reduce the likelihood of complications caused by high blood pressure, such as stroke (when the blood supply to the brain is disturbed).

You may also be prescribed anticonvulsant medication to prevent the convulsions (fits) of eclampsia. Injections of magnesium sulphate can halve the risk of pregnant women developing eclampsia. They can also be used to treat convulsions if they occur.

Premature birth

A baby born before the 37th week of pregnancy is premature and may not be fully developed. However, if the baby is seriously affected by pre-eclampsia or there is a strong risk of further complications, it may be necessary to deliver the baby prematurely, as this is the only way to cure pre-eclampsia.

Attempts will be made to manage pre-eclampsia until after 36 weeks of pregnancy. Some recent research has suggested that once the baby reaches 37 weeks, it may be better to induce labour (start labour artificially), rather than wait and carefully monitor the baby until it is born naturally. This reduces the risk of complications from pre-eclampsia, including HELLP syndrome and eclampsia.

The premature delivery of the baby will usually be done by caesarean section (through an incision in the abdomen). You should be given information about the risks of both premature birth and pre-eclampsia, so that the best decision regarding treatment can be made.

The baby might need to stay in a neonatal intensive care unit. This can replicate the functions of the womb and allow the baby to develop fully. Once it is safe to do so you will be able to take your baby home.

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If pre-eclampsia is not diagnosed and monitored, a number of serious complications can develop.

Although complications from pre-eclampsia are rare, having severe pre-eclampsia or continuing to smoke with pre-eclampsia increases the risk of complications.


Eclampsia is a term that describes a type of convulsion (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 and in the UK there are around 5 cases of eclampsia for every 10,000 births.

During an eclamptic convulsion, the mother’s arms, legs, neck or jaw will twitch involuntarily in repetitive, jerky movements. She may lose consciousness and may wet herself. The convulsions 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 convulsions are severe. Of thoses 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 magnesium sulphate 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 eclampsia.

HELLP syndrome

HELLP syndrome is a combined 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 week 20 of the pregnancy.

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 it 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 is receiving treatment, it is possible for her to make a full recovery. The main danger to the baby is from premature birth (being born before the 37th week of pregnancy).

Premature babies often have a low birth weight and find it hard to breathe on their own. It is likely they will need to stay in neonatal intensive care for close supervision. If the baby’s birth weight is less than 1,500g (3.5lbs), the baby has a one in six chance of dying before their first birthday.

Cerebral haemorrhage

Blood supply to the brain can be disturbed as a result of high blood pressure. This is known as a cerebral haemorrhage, more commonly stroke. If the brain does not get enough oxygen and nutrients from the blood, brain cells will start to die.

Organ problems

  • Pulmonary oedema is where fluid builds up in and around the lungs. This stops them from working properly by preventing them from absorbing oxygen.
  • Kidney failure is when the kidneys cannot filter waste products from the blood, causing toxins and fluids to build up in the body.
  • Liver failure causes 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 (known medically as disseminated intravascular coagulation) and the proteins that control blood clotting become abnormally active.

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