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Pregnant Woman
Jovian Wat, PhD

Approximately 10%​ of pregnant women in Canada have high blood pressure during pregnancy, as discussed in our blood pressure & hypertension article. Preeclampsia is a hypertensive disorder of pregnancy, impacting 5% of all pregnancies. Although preeclampsia is less common than gestational hypertension, preeclampsia is considered a more severe hypertensive disorder of pregnancy.

Keep reading to learn more about preeclampsia.

What is preeclampsia?

Preeclampsia is diagnosed when a pregnant women who had normal blood pressure prior to pregnancy develops high blood pressure after 20 weeks of pregnancy, along with signs of damage to her organs. The most common type of organ damage in women with preeclampsia is kidney damage, however, women with preeclampsia can also show signs of damage to the liver, lungs, heart or brain.

Preeclampsia is sometimes defined as non-severe or severe:

  • Non-severe - more mild symptoms develop near the end of pregnancy

  • Severe - more severe symptoms develop earlier in pregnancy (usually before 34 weeks of pregnancy), including                      systolic blood pressure over 160 mmHg and/or diastolic blood pressure over 110 mmHg

Pregnant women with preeclampsia are at higher risk of adverse pregnancy outcomes, including Caesarean section, small for gestational age baby, placental abruption and preterm birth.

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What is the cause of preeclampsia?


Scientists believe that preeclampsia is caused by the mother's placenta, cardiovascular system and immune system.

During normal pregnancy, the mother’s body undergoes many changes to adapt to pregnancy. This includes the development of the placenta and increased demands on the mom's cardiovascular system to provide proper levels of blood to supply the growing placenta and baby. The placenta and cardiovascular system coordinate during pregnancy by sending protein and other molecular signals to each other to guide these pregnancy changes.

Scientists believe that preeclampsia develops due to a breakdown in communication between the placenta and the rest of mom's body.


The placentas of most women with preeclampsia look and act differently than placentas of pregnant women who have healthy pregnancies. In more scientific terms, the anatomy and physiology of the placenta is typically abnormal in women with preeclampsia. 

Due to these placental abnormalities, the placenta of women with preeclampsia releases abnormal levels of proteins that then enter the mom's circulation and interact with her blood vessels and heart. These proteins from the placenta then interact with the inner cell layer of mom's blood vessels, known as endothelial cells, and can cause damage to these cells. Abnormal signaling by the placenta, damage to the endothelial cells, or a combination of both are thought to cause the symptoms associated with preeclampsia. 

Women who go on to be diagnosed with preeclampsia have higher blood pressures even at 10-17 weeks of pregnancy, when compared to women who continue to have normal blood pressure levels. When compared to pregnant women with normal blood pressure, women with preeclampsia show abnormal levels of resistance in their blood vessels (total peripheral resistance) and amount of blood pumped with each heart beat (cardiac output).

Read here for a more detailed article about the causes of preeclampsia.

Risk factors for preeclampsia


A number of risk factors for preeclampsia have been identified, including factors that relate to mom's placenta, cardiovascular system and immune system. These include:

  • First pregnancy or first pregnancy with new partner

  • Obesity

  • Advanced maternal age​

  • Ethnicity

  • Twin birth

  • In vitro fertilization

  • History of preeclampsia in previous pregnancy

  • Family history of preeclampsia

  • Family history of early-onset cardiovascular disease

  • Pre-existing cardiovascular or kidney disease

Symptoms of preeclampsia


Preeclampsia is associated with a range of symptoms, including:

  • Headaches

  • Dizziness

  • Difficulty breathing

  • Swelling & weight gain

  • Pain in upper abdomen 

  • Blurred vision or other changes in eyesight

  • Nausea & vomiting

Testing & investigations for preeclampsia


Clinical testing can help to identify women who are at higher risk of developing preeclampsia, in addition to assessing the clinical risk factors (listed above). Doppler ultrasound can determine if pregnant woman have abnormal placental structure or function, which can indicate higher risk of severe preeclampsia.

Some hospitals now offer blood tests that can measure levels of proteins produced by the placenta in the mom's blood. Levels of these proteins in the mom's blood, including levels of placental growth factor, are highly predictive of preeclampsia and provide doctors with insight into how the mom's placenta is functioning. 

Read more here to learn about placental growth factor testing for preeclampsia screening.

Blood pressure monitoring is a standard practice for pregnant women in Canada and should be measured regularly at clinical appointments. High blood pressure is defined as:

  • Non-severe - systolic blood pressure between 140-159 mmHg and/or diastolic blood pressure over 90-109 mmHg

  • Severe - systolic blood pressure over 160 mmHg and/or diastolic blood pressure over 110 mmHg

If pregnant women have high blood pressure, they will also be checked for other symptoms of organ injury to determine if a women has gestational hypertension or preeclampsia. This typically includes testing urine for signs of kidney injury and testing blood for signs of other organ injury. Pregnant women with preeclampsia will show signs of organ injury, usually proteinuria (kidney damage). 

Doctors will check for evidence of:

  • Proteinuria: check for high protein levels in the urine

  • Renal insufficiency: check for high creatinine levels in the blood

  • Thrombocytopenia: check for low platelet levels in the blood

  • Impaired liver function: check for high liver enzyme levels in the blood

  • Pulmonary edema: ask women about symptoms

  • Cerebral or visual disturbances: ask women about symptoms

Doctors will also monitor the baby to ensure that growth and development are normal. This includes fetal heart rate, blood flow through the umbilical cord and blood flow in the brain. Studies have shown that pregnant women with hypertension tend to have smaller babies, compared to pregnant women with normal blood pressure. These investigations will let doctors know if the baby is being impacted by mom’s high blood pressure and if early delivery should be considered to ensure the health of the baby​.

A Toddler and a Baby
Cheerful Pregnant Woman
Treatment & management of preeclampsia


When preeclampsia develops in pregnant women, the disease will persist and symptoms will typically become worse until delivery. The Society of Obstetricians and Gynaecologists of Canada recommends that women with preeclampsia should see their doctor once a week for monitoring.

Treatment & management of preeclampsia is centered around ensuring the safety of mom and baby. Doctors will also try to avoid the need for intensive care for the baby when it is born.


Hospital admission and delivery are recommended for pregnant women with preeclampsia if they are:

  • More than 37 weeks pregnant

  • Have suspected placental abruption

  • More than 34 weeks pregnant with unstable mom or baby conditions, such as:

    • Ongoing labor or membrane rupture​

    • Baby weight less than 5th centile

    • Oligohydramnios 

    • Low fetal biophysical profile

    • Maternal complications (ie. pulmonary edema)

Pregnant women who are not immediately delivered will continue fetal monitoring, blood pressure monitoring and blood tests. Women are recommended to monitor their own symptoms closely, as well as fetal movements. If women with severe symptoms of preeclampsia are less than 34 weeks pregnant, corticosteroids will be given to help promote lung maturation in the baby, in case the baby needs to be induced pre-term. 

Pregnant women with preeclampsia are not recommended to make other lifestyle changes, such as salt restriction or workload reduction.

Doctors will try to maintain blood pressure of women with drugs called ‘anti-hypertensives’ to lower mom’s blood pressure.


In cases of severe preeclampsia, doctors will give pregnant women magnesium sulfate to prevent eclampsia (seizures). If pregnant women develop complications of preeclampsia known as HELLP syndrome (hemolysis, elevated liver enzymes, and a low platelet count), delivery is recommended following stabilization of the mom.

The American College of Obstetricians and Gynecologists state that the mode of delivery for women with preeclampsia should be determined by both fetal and maternal factors; not all women with preeclampsia need to deliver via Cesarean section. 

Prevention of preeclampsia

In pregnant women with low calcium intake, calcium supplementation lowers the risk of all hypertensive disorders of pregnancy, including preeclampsia.


Recent research shows that aerobic exercise during pregnancy is associated with lower incidence of hypertension in pregnancy, when compared to pregnant women who did not exercise (5.9% vs 8.5%). A recent meta-analysis reported that exercise in pregnancy reduces the risk of developing hypertension in pregnancy by over 75%. Read more about exercise in pregnancy here.

Pregnant women at low-risk of preeclampsia may benefit from a multivitamin with folate and exercise for the prevention of preeclampsia.

Low-dose aspirin (75-100mg) is recommended for pregnant women at high-risk of developing preeclampsia, starting before 16 weeks of pregnancy. Controlling weight before pregnancy, increased home rest and stress reduction may also be useful for preeclampsia prevention in high-risk women. Read more about aspirin for preeclampsia prevention here.

Interested in learning more about preeclampsia research?

The American Heart Association is a leading publisher of new and exciting preeclampsia research. Here is a recent article reviewing the latest scientific theories and research in the world of preeclampsia.


Preeclampsia is a common hypertensive disorder of pregnancy that impacts approximately 5% of pregnancies. Preeclampsia is thought to be caused by the interaction of mom's placenta, cardiovascular system and immune system. Treatment for preeclampsia focuses on controlling mom's symptoms and ensuring maternal and fetal safety. Delivery is recommended for pregnant women with preeclampsia above 37 weeks of pregnancy.


Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.

This article was written by Dr. Jovian Wat and edited by Dr. Kelsey McLaughlin and Dr. Melanie Audette.

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