What is pre-eclampsia?

Pre-eclampsia is unique to pregnancy and affects 2-3% of pregnancies. It is defined by two features: new-onset high blood pressure and protein in the urine. Not all women with pre-eclampsia have both features: some develop a complication of pre-eclampsia associated with one feature. Complications of pre-eclampsia include injury to the kidneys or liver, fluid on the lungs or brain, problems with blood clotting, poor growth of the unborn baby and stillbirth. A severe complication of pre-eclampsia is eclampsia, when a woman with pre-eclampsia has seizures or fits. Pre-eclampsia can only occur in the second half of pregnancy (after 20 weeks) or after the baby is born.

What causes pre-eclampsia?

Currently, we do not know what causes pre-eclampsia, which makes it difficult to diagnose and treat. Pre-eclampsia is the subject of much ongoing research and is believed to originate from the placenta (or afterbirth).

We can tell this because pre-eclampsia usually improves after the placenta is delivered, and because abnormal pregnancies where there is no baby (e.g. molar pregnancies) still develop pre-eclampsia. Blood from mother and baby meet in the placenta, allowing exchange of gases, food and waste products. Pre-eclampsia is associated with abnormal development of the blood vessels on the mother’s side of the placenta early in pregnancy, called spiral arteries. The placenta then becomes stressed later in pregnancy, causing clinical symptoms in the mother, though exactly how this happens is still not well understood.

What are the signs and symptoms of pre-eclampsia?

Pre-eclampsia can cause headaches, problems with vision (such as flashing or blurring), severe pain beneath the ribs, vomiting, or sudden swelling of the hands and feet (peripheral oedema). Many women with pre-eclampsia do not feel unwell at all; it is detected when they visit their doctor or midwife and their blood pressure and urine are routinely checked.

What increases your risk of pre-eclampsia?

Factors which increase the risk of pre-eclampsia are asked about when a woman first meets her midwife in pregnancy (the “booking visit”). Women at high risk include those with previous high blood pressure in pregnancy, high blood pressure outside pregnancy, type 1 or 2 diabetes, chronic kidney disease, and autoimmune diseases, such as lupus or antiphospholipid syndrome. Women at moderate risk include those in their first pregnancy, age 40 years or older, obese with a body mass index of 35 kg/m² or greater, those whose last pregnancy was 10 or more years ago, twin or triplet pregnancies, and women whose mothers or sisters have had pre-eclampsia.

What can pregnant women do to reduce their risk of developing pre-eclampsia?

Women at higher risk of pre-eclampsia will be told so by their midwife and advised to start taking a low dose of aspirin from 12 weeks of pregnancy to prevent pre-eclampsia. Women who are not at higher risk will not benefit from taking this medication; we do not know how it prevents pre-eclampsia. All women can reduce their risk of undiagnosed pre-eclampsia by attending their routine doctor and midwife appointments and having their blood pressure and urine checked.

What happens when a woman is suspected to have pre-eclampsia?

If a woman’s midwife or doctor is worried that she may have pre-eclampsia, they will usually send her to the hospital for assessment by a specialist. Here her blood pressure and urine will be checked again and, if abnormal, her urine will be sent to the laboratory for more accurate testing. Women suspected to have pre-eclampsia will have blood tests taken and, if more than 26 weeks pregnant, will have their baby’s heart tracing recorded. Many women who are diagnosed with pre-eclampsia are admitted to hospital for a period of time. Some hospitals are introducing a new blood test to rule out pre-eclampsia in those referred to hospital, preventing unnecessary stays.

Treatments for pre-eclampsia

High blood pressure can be treated with a number of different medications that are known to be safe in pregnancy. These are usually tablets and can be taken once per day or more frequently. Once blood pressure medication is started, regular monitoring is required, as the dose might need to increase.

The only cure for pre-eclampsia is to deliver the baby and placenta. Deciding the best time to deliver the baby involves carefully balancing the risks to both mother and baby of continuing the pregnancy with the risks of delivering the baby early. As a consequence, women diagnosed with pre-eclampsia (and their babies) will usually be monitored closely with blood pressure measurements, blood tests and extra heart tracings and scans. If a woman is diagnosed with pre-eclampsia at the end of pregnancy (when her baby is fully grown), there is often no benefit to continuing the pregnancy, so her labour may be induced straight away.

Complications of pre-eclampsia

HELLP syndrome
HELLP syndrome is an acronym for three common complications of pre-eclampsia:
Haemolysis (bursting of red blood cells), Elevated Liver enzymes (associated with liver damage) and Low Platelets (which can mean blood is less able to clot). Treatment for HELLP syndrome usually involves close monitoring of blood tests and, when they become very abnormal, delivery of the baby.

Eclampsia
Eclampsia refers to seizures or fits in women with pre-eclampsia. These are of the “grand mal” type, meaning the woman loses consciousness and her body shakes. Like all complications of pre-eclampsia, eclampsia can only happen during the second half of pregnancy or after the baby is born. Seizures due to eclampsia will usually stop themselves, but drugs are given to prevent further seizures. If a woman is still pregnant and develops eclampsia, her baby will be delivered as soon as it is safe to do so.

Fetal growth restriction
The babies of some women with pre-eclampsia will grow less than expected – a condition referred to as fetal growth restriction. This might be identified by routine measurements of the mother’s womb taken with a tape measure on the skin, or on an ultrasound scan. There is no specific treatment for fetal growth restriction: the baby is monitored closely and delivery is recommended when the risk of stillbirth is felt to be too high.

Stillbirth
Five per cent of stillbirths that occur in babies without an abnormality occur in women with pre-eclampsia. While stillbirth is still uncommon in pre-eclampsia, it is difficult to predict. The only preventative measure is to deliver the baby early.

Preterm birth
Ten percent of all preterm births (before 37 weeks) occur because of pre-eclampsia. This is usually because labour has been induced or caesarean section has been performed early, rather than occurring spontaneously. An early birth carries a higher rate of complications for the baby, and so doctors will only recommend early delivery if they think it is safer for mother and/or baby.

What are the implications of pre-eclampsia after the baby is born?

Immediately after birth, women with pre-eclampsia will often need to stay in hospital for a few days. This is to confirm that any complications of pre-eclampsia resolve and that blood pressure treatment is appropriate. Blood pressure often rises in the first few days after delivery, so regular monitoring is required, even once home. Most women will have stopped taking blood pressure medications within a few weeks of leaving the hospital.

Women who have had pre-eclampsia are at higher risk of developing high blood pressure or pre-eclampsia in a future pregnancy. This usually results in advice to take aspirin from 12 weeks in a future pregnancy, but a midwife will assess this at the first appointment in the next pregnancy. There is also a greater risk of developing high blood pressure and complications of this, such as heart disease, later in life. There is not currently any specific advice on how to reduce this risk in women who have had pre-eclampsia. Maintaining a healthy diet, exercising, not being overweight and not smoking will reduce the risk of high blood pressure and heart disease for all women.

Main Points

• Pre-eclampsia is unique to pregnancy and affects 2-3% of pregnancies.
• It is defined by new-onset high blood pressure and protein in urine.
• Symptoms include headaches, problems with vision (such as flashing or blurring), severe pain beneath the ribs, vomiting, or sudden swelling of the hands and feet (oedema).
• Complications of pre-eclampsia can be severe: they include injury to the kidneys or liver, fluid on the lungs or brain, problems with blood clotting, poor growth of the unborn baby and stillbirth. Pre-eclampsia can also lead to eclampsia, which causes seizures.
• The cause of pre-eclampsia is not known, but medical professionals believe it to be related to the placenta.
• Pre-eclampsia is diagnosed through the use of blood and urine tests routinely performed at midwife appointments.
• Women with previous high blood pressure in pregnancy, high blood pressure outside pregnancy, type 1 or 2 diabetes, chronic kidney disease, and autoimmune diseases, such as lupus or antiphospholipid syndrome, are at high risk of developing pre-eclampsia. Women who’re obese, carrying twins or more, or are aged over 40 also are at increased risk.
• Women at higher risk of pre-eclampsia will be advised to start taking a low dose of aspirin from 12 weeks of pregnancy to prevent pre-eclampsia.
• Many women who are diagnosed with pre-eclampsia are admitted to hospital for a period of time.
• The only cure for pre-eclampsia is to deliver the baby and the placenta. The risks of continuing the pregnancy will have to be weighed against the risks of delivering the baby early.
• After giving birth, women with pre-eclampsia will need to stay in the hospital for a few days.
• Having pre-eclampsia in one pregnancy makes it more likely that it will occur again in a future pregnancy. Maintaining a healthy diet, exercising, having a BMI in the healthy range, and not smoking all reduce the risk of high blood pressure as well as heart disease.

References

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C. W. G. Redman, Rev. Med. Interne. 32, 41–44 (2011).

National Institute for Health and Care Excellence, NICE Guid. (2010).

American College of Obstetricians and Gynecologists. Task Force on Hypertension in Pregnancy, Obstet. Gynecol. 122, 1122–1131 (2013).

S. Robson, W. Martin, R. Morris, R. Coll. Obstet. Gynaecol. (2013).

National Institute for Health and Care Excellence, PlGF-based testing to help diagnose suspected pre-eclampsia: Diagnostics Guidance 23. NICE Guid. (2016), pp. 1–46.

L. Duley, D. Henderson-Smart, S. Meher, J. King, Cochrane Database Syst. Rev. (2007).