The Facts

Preeclampsia is a condition that some people experience during pregnancy. Preeclampsia occurs after week 20 of pregnancy and is characterized by an increase in blood pressure (hypertension) and either high levels of protein in the urine (proteinuria) or end-organ damage. This condition used to be called toxemia of pregnancy.

Preeclampsia can also cause swelling, particularly in the face and hands. This swelling can lead to weight gain outside of the normal weight gain expected during pregnancy. It may also be accompanied by other symptoms such as blurred vision, headache, nausea, and pain in the upper abdomen.

About 3% to 7% of pregnancies are complicated by preeclampsia. Preeclampsia can be either mild or severe. Approximately 1 in 200 people with mild preeclampsia go on to have full-blown eclampsia, a condition leading to seizures that can be fatal to both birth parent and fetus. As many as 1 in 50 people with severe preeclampsia may develop a seizure. Preeclampsia and eclampsia remain leading causes of maternal death in childbirth.

People who have high blood pressure before pregnancy have a higher risk of miscarriage or giving birth to babies that are premature, underweight, or stillborn. People who develop high blood pressure while pregnant (about 7% of pregnancies) run a slightly higher risk of these complications, and those with preeclampsia run the highest risk of all.


The causes of preeclampsia remain unknown. There are a few theories, and certain characteristics that are more common in sufferers. However, the cause is not yet known.

We do know some risk factors. For example, preeclampsia tends to run in families, just like typical chronic high blood pressure. It's also more common in racial groups that are especially susceptible to high blood pressure, notably people of African descent. This might suggest that people who are genetically susceptible to high blood pressure are more likely to develop preeclampsia.

The known risk factors for preeclampsia are:

  • being over the age of 35 to 40, or under 20
  • first pregnancy
  • preeclampsia in previous pregnancies
  • multiple fetuses (e.g., twins, triplets)
  • non-Hispanic Black ancestry or Indigenous ancestry
  • family history of preeclampsia
  • diabetes
  • preexisting high blood pressure, kidney disease, or blood disorders
  • being overweight before pregnancy

Symptoms and Complications

Technically, preeclampsia is mild if blood pressure is over 140/90 mm Hg (see our condition article on high blood pressure), or if it rises by more than a certain amount and there is protein in the urine or swelling of the hands, ankles, and feet. Severe preeclampsia is diagnosed when blood pressure is over 160/110 mm Hg, accompanied by severe proteinuria, severe headache, abdominal pain, visual problems, shortness of breath, confusion, or decreased growth of the baby.

Visual problems may occur because high blood pressure stresses the retina, pushing it forward. In extreme cases, this can lead to retinal detachment and possibly blindness.

The baby's growth may be affected because high blood pressure can affect how much blood flows through the placenta to the baby. Recently, autism and developmental delay have both been linked to severe preeclampsia.

With preeclampsia, a person's reflexes become unusually active. Increasing blood pressure will lead to increasing hyperreflexia (overactive reflexes), until eventually uncontrollable seizures result.

Severe complications of preeclampsia include:

  • eclampsia – potentially fatal seizures caused by high intracranial (in the head) blood pressure
  • cerebral (brain) hemorrhage (stroke) due to burst blood vessels in the brain (the main cause of maternal death)
  • retinal detachment, which may lead to blindness
  • ruptured liver
  • accumulation of fluid in the lungs (pulmonary edema)
  • abruptio placentae – the placenta separates from the wall of the uterus and internal bleeding occurs where it had been attached. The bleeding may be life-threatening to both the birth parent and the fetus.
  • kidney failure in the birth parent
  • HELLP syndrome – this stands for hemolysis, elevated liver enzymes, and low platelet count. Hemolysis is destruction of red blood cells in the liver. It's a normal bodily function, but when it speeds up, as in HELLP syndrome, the cells are killed faster than they can be replaced and anemia is the result. Elevated liver enzymes are a sign of an inflamed or overactive liver. Platelets are tiny blood components largely responsible for clotting blood. Any time that the blood is low in clotting agents (such as platelets), the risk of hemorrhage (bleeding) increases, especially in the brain.

Making the Diagnosis

We don't know what causes preeclampsia, so we define it by its symptoms.

If a pregnant person's blood pressure is over a certain level (140/90 mm Hg) and they have proteinuria (protein in the urine), they have mild preeclampsia. If the blood pressure goes higher still (more than 160/110 mm Hg), and proteinuria is present and other symptoms appear (such as headache, eye problems, abdominal pain, or decreased growth of the baby), they have severe preeclampsia.

If they have a seizure, then they have eclampsia. If their liver, kidney, or blood function is abnormal, then they have HELLP.

Treatment and Prevention

Doctors and hospitals take preeclampsia very seriously. Typically only in the mildest of cases, where high blood pressure can be measured but doesn't cause any symptoms, is the individual allowed to return home – and only on the condition that they go straight to bed and stay there. If there's no improvement in a couple of days, they’ll be admitted to the hospital for observation.

Lying down for long periods reduces blood pressure. In addition, the individual may be told to lie on their left side. This decreases pressure on several major blood vessels and increases the desire to urinate. Regular urination improves the quality of the circulating blood. It is recommended to drink plenty of liquids. Salt intake should not be reduced – while this is a good idea for chronic high blood pressure, salt is needed during pregnancy.

Medications normally used to control high blood pressure are not used to treat preeclampsia. Instead, magnesium sulphate is injected. This reduces hyperreflexia and reduces the chance of seizures. It also lowers blood pressure at the same time. The same medication is given for full-blown eclampsia. If the blood pressure is not controlled with magnesium sulphate alone, injectable blood pressure medications called labetalol* and hydralazine may be used.

Magnesium sulphate helps to control the symptoms and reduces the risk of fatal complications, but the only thing that will pull the birth parent and baby out of the danger zone is to deliver as quickly as possible. Even if the baby is premature, its chances are better "on the outside." Babies are only left in place when the birth parent's blood pressure is responding to treatment and the baby is clearly too small to survive outside the womb.

If the baby is big enough, and the birth parent 's condition has been stabilized with magnesium sulphate, the doctor will usually give medications to stimulate labour. If for any reason a normal birth poses problems, a caesarean section will be recommended. A prompt delivery reduces the risk of complications for both the birth parent and the baby and is the only cure for preeclampsia.

The birth parent should be re-evaluated within one week after they have delivered the baby and been discharged from the hospital. Sometimes preeclampsia reoccurs up to 4 weeks after delivery, but usually blood pressure falls steadily from the moment the baby is delivered. Blood pressure usually returns to normal within a few months.

Those with high risk factors for preeclampsia may be recommended by their doctor to take low-dose ASA* starting the second trimester and up until delivery to prevent preeclampsia.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

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