High Blood Pressure During Pregnancy

Blood pressure is the force of the blood pushing against the walls of the arteries (blood vessels that carry oxygen-rich blood to all parts of the body). When the pressure in the arteries becomes too high, it is called hypertension.

Up to 5 percent of women have hypertension before they become pregnant.¹ This is called chronic hypertension. Another 5 to 8 percent develop hypertension during pregnancy.² This is referred to as gestational hypertension. Gestational hypertension generally goes away soon after delivery; however, women who develop it may be at increased risk of developing hypertension later in life.

High blood pressure usually causes no noticeable symptoms, whether or not a woman is pregnant. However, hypertension during pregnancy can cause serious complications for mother and baby. Fortunately, serious problems usually can be prevented with proper prenatal care.

A pregnant woman’s blood pressure is measured at each prenatal visit. The health care provider measures blood pressure with an inflatable cuff that wraps around the upper arm. The pressure in the arteries is measured as the heart contracts (systolic pressure) and when the heart is relaxed between contractions (diastolic pressure). The blood pressure reading is given as two numbers, with the top number representing the systolic and bottom number the diastolic pressure—for example, 110/80. A systolic reading of 140 or higher, or a diastolic reading of 90 or higher is considered high blood pressure. Because blood pressure can go up and down during the day, health care providers often re-check a high reading with one or more additional readings to determine if a woman truly has high blood pressure

Chronic hypertension is defined as high blood pressure that is diagnosed before pregnancy or before the 20th week of pregnancy. This form of hypertension does not go away after delivery.

The causes of chronic hypertension are not thoroughly understood, although heredity, diet and lifestyle are believed to play a role. Untreated hypertension can increase the risk of serious health problems such as heart attack and stroke.

Women with chronic hypertension should see their health care provider before attempting to conceive. A pre-pregnancy visit allows the provider to ensure that the blood pressure is under control, and to evaluate any medication the woman takes to control her blood pressure. While some medications to lower blood pressure are safe during pregnancy, others—including a group of drugs called angiotensin-converting-enzyme (ACE) inhibitors—can harm the fetus. Some women with chronic hypertension may be able to stop taking their medication or reduce their dose, at least during the first half of pregnancy, as blood pressure tends to fall during this time. However, blood pressure needs to be monitored carefully during this period.

Most women with chronic hypertension have healthy pregnancies. However, about 25 percent develop a form of gestational hypertension called preeclampsia (see below), which poses special risks.^2,3

There are two main forms of gestational hypertension. Both occur after the 20th week of pregnancy and go away without treatment soon after delivery. Preeclampsia is a potentially serious disorder, which is characterized by high blood pressure and protein in the urine. When high blood pressure is not accompanied by protein in the urine, it is referred to as gestational hypertension. However, gestational hypertension may progress to preeclampsia, so all women who develop high blood pressure in pregnancy are monitored closely.

Preeclampsia also may be accompanied by swelling (edema) of the hands and face and sudden weight gain (5 or more pounds in one week). Other signs of preeclampsia include blurred vision, severe headaches, dizziness and intense stomach pain. A pregnant woman should contact her health care provider right away if she develops any of these symptoms.

Preeclampsia usually occurs after about 30 weeks of pregnancy. Most cases are mild, with blood pressure around 140/90. Women with mild preeclampsia often have no obvious symptoms. If left untreated, though, preeclampsia can cause serious problems.

It’s important to remember that many women who develop preeclampsia or gestational hypertension do so at term (at or beyond 37 weeks of gestation). These women generally have few complications.

What risks do preeclampsia and other forms of hypertension pose for a pregnant woman and her fetus?
All forms of hypertension can constrict the blood vessels in the uterus that supply the fetus with oxygen and nutrients. When this occurs before term, it can slow the fetus’s growth, sometimes resulting in low birthweight. Hypertension also increases the risk of pretermdelivery (before 37 weeks gestation). Premature and low-birthweight babies face an increased risk of health problems during the newborn period and lasting disabilities, such as learning problems and cerebral palsy.

Women with hypertension also have an increased risk of placental abruption,  which is separation of the placenta from the uterine wall before delivery. Severe abruption can cause heavy bleeding and shock, which are dangerous for both mother and baby. The most common symptom of abruption is vaginal bleeding after 20 weeks of pregnancy. A pregnant woman always should report any vaginal bleeding to her health care provider immediately. While all women with high blood pressure during pregnancy face some increased risk of abruption and the other complications discussed above, the risk is greatest in women who have preeclampsia along with chronic high blood pressure.³

Preeclampsia also can quickly progress to a rare but life-threatening condition called eclampsia, causing seizures and sometimes coma. Fortunately, eclampsia is rare in women who receive regular prenatal care. At each prenatal visit, blood pressure is measured and urine is checked for protein, so that preeclampsia can be diagnosed and treated before it can progress to eclampsia.

The only cure for preeclampsia is delivery. However, this is not always best for the baby. So treatment depends upon how severe the problem is and how far along a woman is in her pregnancy. If a woman is at term (37 to 40 weeks), the preeclampsia is mild, and her cervix has begun to thin and dilate (signs that it’s ready for delivery), her health care provider probably will recommend inducing labor. This prevents any potential complications that could develop if the pregnancy continues and the preeclampsia worsens. If her cervix is not yet ready for labor, her provider may recommend medication to help prepare her cervix for induction or continue to monitor her and her baby closely until labor starts on its own.

If a woman develops mild preeclampsia before her 37th week, her provider probably will recommend that she reduce her activities.  In some cases, hospitalization may be recommended, though most women can be treated at home. Her baby’s well-being will be closely monitored with tests such as ultrasound and fetal heart rate monitoring. Blood tests probably will be recommended for the pregnant woman to see if the preeclampsia is progressing and harming her health.

If a woman has severe preeclampsia, she should be hospitalized. Her health care provider will probably recommend inducing labor if she is beyond 33 to 34 weeks gestation.⁴At this stage of pregnancy, the risk of prematurity is generally outweighed by the risk of progression to eclampsia. Before inducing labor, doctors generally treat women who are at less than 34 weeks gestation with a drug called a corticosteroid that helps speed maturity of the fetal lungs to reduce the risk of prematurity-related problems. A woman who develops severe preeclampsia at less than 32 weeks gestation sometimes can be monitored closely in the hospital, to prolong the pregnancy safely while her baby matures.

Sometimes, a woman’s blood pressure continues to rise despite treatment with blood pressure medications, and her baby must be delivered early to prevent serious health problems in the mother, such as stroke, liver damage and seizures. Babies born early may have difficulties due to prematurity, such as trouble breathing. Most of these infants will do better in an intensive care nursery than if they had stayed in the uterus.

About 10 percent of women with severe preeclampsia also develop a disorder called HELLP (an acronym for Hemolysis, Elevated Liver enzymes, and Low Platelet count) syndrome, which is characterized by blood and liver abnormalities.⁵Symptoms may include nausea and vomiting, headache, upper abdominal pain and general malaise. Women with HELLP syndrome, which also can develop in the first 48 hours after delivery, are treated with medications to control blood pressure and prevent seizures, and sometimes with blood transfusions. Women who develop HELLP syndrome during pregnancy almost always require early delivery to prevent serious complications.

Most of these women have successful pregnancies. Their health care providers monitor their blood pressure and urine carefully for signs of preeclampsia or worsening hypertension. Tests such as ultrasound and fetal heart rate testing may be recommended to check on fetal growth and well-being. If tests are normal, they may not need to be repeated unless the mother’s condition changes. The provider may recommend that the pregnant woman cut back on her activities and avoid aerobic exercise.

A vaginal delivery is preferable to a cesarean for a woman with preeclampsia because it avoids the added stresses of surgery. It generally is appropriate for women with preeclampsia to have epidural anesthesia for pain relief during labor and delivery.

Women with severe preeclampsia or eclampsia generally are treated with a drug called magnesium sulfate to help prevent seizures during labor and delivery. It is less clear whether women with mild preeclampsia benefit from this drug.

Doctors do not know what causes preeclampsia. However, women are more susceptible if they have any of these risk factors^1,3:

• First pregnancy 
• Family history of preeclampsia 
• Personal history of chronic high blood pressure, kidney disease, diabetes, systemic lupus erythematosus (a disease often characterized in its early stages by arthritis-like stiffness, a butterfly-shaped rash across the nose and cheeks, fatigue and weight loss), and certain thrombophilias 
• Multiple pregnancy 
• Age less than 20 years, or over 35 
• African-American 
• Higher than normal weight 
• Personal history of preeclampsia 

Women who have had preeclampsia are more susceptible to developing it again in another pregnancy. The risk of recurrence appears to be highest when preeclampsia has occurred before the 29th week of gestation and, in some cases, may be as high as 65 percent in another pregnancy.⁵ About 20 percent of women who have developed preeclampsia after the 37th week of pregnancy develop it again.⁵

Currently, there is no way to prevent preeclampsia or gestational hypertension. However, a 1999 British study suggested that some high-risk women (including women who had preeclampsia in a previous pregnancy) may be able to reduce their risk of preeclampsia by taking vitamins C and E through the second half of pregnancy.⁶The high-risk women who took the vitamins reduced their risk of developing preeclampsia by about 75 percent. The researchers caution that more studies are needed before this treatment can be widely recommended. Other treatments that looked promising in early studies (such as aspirin and calcium) have not proven helpful in preventing preeclampsia.

Does the March of Dimes fund research on preeclampsia and other forms of high blood pressure in pregnancy?
The March of Dimes has supported a number of studies aimed at improving understanding of the causes of preeclampsia and at improving treatment for this and other types of high blood pressure in pregnancy. Recent grantees have been seeking to identify genes that may play a role in preeclampsia to identify susceptible women earlier in pregnancy and, ultimately, devise ways to prevent this disorder. Another grantee has been investigating whether certain fatty acids found in fish, such as salmon and mackerel, may help reduce the risk of preeclampsia.

1. American College of Obstetricians and Gynecologists. Chronic Hypertension in Pregnancy. ACOG Practice Bulletin, number 29, July 2001.

2. American College of Obstetricians and Gynecologists. Diagnosis and Management of Preeclampsia and Eclampsia. ACOG Practice Bulletin, number 33, January 2002.

3. Roberts, J.M., et al. Summary of the NHLBI Working Group on Research on Hypertension During Pregnancy. Hypertension, volume 41, March 2003, pages 437-445.

4. Sibai, B.M. Diagnosis and Management of Gestational Hypertension and Preeclampsia. Obstetrics and Gynecology, volume 102, number 1, July 2003, pages 181-192.

5. Moldenhauer, J.S. and Sibai, B.M. Hypertensive Disorders of Pregnancy, in Scott, J.R. et al (eds): Danforth’s Obstetrics and Gynecology, Ninth Edition. Philadelphia, Lippincott Williams & Wilkins, 2003, pages 257-271.

6. Chappell, L.C., et al. Effect of Antioxidants on the Occurrence of Preeclampsia in Women at Increased Risk: A Randomized Trial. Lancet, volume 354, September 4, 1999, pages 810-816.

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