NHLBI publishes update on high blood pressure in pregnancy

October 23, 2000

The National High Blood Pressure Education Program (NHBPEP) Coordinating Committee has issued new guidance for clinicians on high blood pressure in pregnancy. The "2000 Working Group Report on High Blood Pressure in Pregnancy" clarifies how to monitor and treat pregnant women who have hypertension prior to pregnancy and those who develop hypertension during gestation. The NHBPEP is coordinated by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health.

"Hypertension during pregnancy is a serious public health concern," says NHLBI Director Dr. Claude Lenfant. "Identifying and preventing complications can be challenging, particularly because our understanding of the causes of these problems is limited. Our goal is to provide a tool to help clinicians assess, monitor, and manage high blood pressure and related conditions for the health and well-being of both mother and child."

Hypertensive disorders occur in 6 to 8 percent of pregnancies and contribute significantly to serious complications for both the fetus and the mother. Fetal complications include severe growth restriction and death (still-birth). In addition, hypertensive disorders account for nearly 15 percent of maternal deaths in the United States, ranking second only to embolism as a leading cause. Other complications for the mother can affect kidney, liver, and central nervous system function.

The new report covers the pathophysiology of hypertensive disorders in pregnancy, patient counseling for future pregnancies, and recommendations for future research. Treatments of women with related conditions, such as renal disease, are also addressed.

The report expands upon the NHBPEP's 1997 high blood pressure treatment guidelines and updates its 1990 report on hypertension in pregnancy. Recommendations are based on evidence-based medicine and consensus among leaders in the field. The NHBPEP is a federation of 45 professional, voluntary, and official agencies.

The report stresses the need for clinicians to differentiate between hypertension (blood pressure equal to or greater than 140 mm Hg systolic or 90 mm Hg diastolic) and hypertension with proteinuria (protein in the urine) - the strongest indicator of preeclampsia. Preeclampsia is a pregnancy-specific and systemic syndrome that affects the placenta, kidney, liver and brain. It can develop gradually or appear suddenly, and it can range from mild to severe. In its most severe form preeclampsia can lead to eclampsia, or maternal seizures, which can result in death.

The 2000 Working Group Report has added the category "gestational hypertension" to its classifications of hypertensive disorders of pregnancy. This term is used on an interim basis to describe women with elevated blood pressure that first appears during midpregnancy without proteinuria; the diagnosis is updated postpartum to either transient hypertension of pregnancy (blood pressure has returned to normal) or chronic hypertension (blood pressure remains elevated).

Other classifications used in the report are:
• Chronic hypertension: Hypertension that is present and observable before pregnancy or diagnosed before the 20th week of gestation.
• Preeclampsia-eclampsia: Hypertension with proteinuria that develops during pregnancy.
• Preeclampsia superimposed upon chronic hypertension.

The report updates a recommendation on measuring diastolic blood pressure during pregnancy, suggesting that clinicians use K5 (disappearance) of the Korotkoff sound over K4 (muffling). Furthermore, gestational hypertension should be determined on the basis of at least two readings.

The causes of gestational hypertension and preeclampsia remain unknown, and standard screening tests or markers for preeclampsia remain somewhat elusive. However, the report identifies several indicators that point to the possibility of preeclampsia in women without chronic hypertension. These include elevated blood pressure and proteinuria occurring for the first time during pregnancy (after 20 weeks gestation) and rising levels of serum creatinine, uric acid, and transaminase levels.

In contrast to earlier guidelines, edema is no longer recognized as a diagnostic criterion for preeclampsia because it appears in too many normal pregnant women to be discriminant for this condition. In addition, the use of blood pressure increases of 30 mg Hg systolic or 15 mm Hg diastolic is no longer recommended.

Women with pre-existing (chronic) or early hypertension are at increased risk of preeclampsia, notes the report, and the prognosis for mother and fetus is worse than in cases in which hypertension first develops during pregnancy. Nearly one in four hypertensive women will develop preeclampsia during pregnancy, typically during midpregnancy. Those who have proteinuria early in their pregnancy are at increased risk for fetal loss and other complications independent of preeclampsia.

Signs of preeclampsia in these women include onset of proteinuria and a sudden increase in blood pressure if hypertension was previously well controlled. However, clinicians may have difficulty distinguishing between changes in blood pressure and early signs of preeclampsia.

"Detecting preeclampsia in women with chronic hypertension can be particularly challenging," notes Dr. Ray Gifford, Jr., of the Cleveland Clinic Foundation, who chaired the NHBPEP Working Group. "Because the consequences of missing a diagnosis of preeclampsia are dire, we encourage clinicians to overdiagnose if necessary."

According to the report, most women with chronic hypertension prior to pregnancy have Stage 1 or 2 hypertension (systolic blood pressure of 140 to 179 mm Hg or diastolic blood pressure of 90 to 109 mm Hg). Whenever possible, they should be evaluated before pregnancy to assess the severity of their hypertension and possible organ damage, and counseled as appropriate. Lifestyle changes regarding physical activity, weight loss, and sodium restriction should also be addressed.

Many patients with chronic hypertension may be able to control their blood pressure without medications or with less medication than used prior to gestation. The report suggests that, if needed, however, most antihypertensive medications - except angiotensin-converting enzyme inhibitors and angiotensin II receptor agonists -can be used safely during pregnancy.

Management of preeclampsia is based first on preventing maternal complications, and second on encouraging growth and maturation of the fetus and allowing the cervix to prepare for delivery -- the only definitive treatment of the condition. The Working Group Report identifies key indications for delivery in preeclampsia, such as gestational age (equal to or greater than 38 weeks) and low platelet count.

Hypertension and signs of organ dysfunction associated with preeclampsia typically disappear within six weeks of delivery. However, women with early-onset preeclampsia or preeclampsia in more than one pregnancy are more likely to develop hypertension later in life.
The "2000 Working Group Report on High Blood Pressure in Pregnancy" was published as a supplement in the July 2000 issue of The American Journal of Obstetrics and Gynecology. The report can be ordered through the NHLBI Information Center at NHLBIinfo@rover.nhlbi.nih.gov or (301) 592-8573.

NHLBI press releases, scientific resources, and other materials are online at www.nhlbi.nih.gov.

NIH/National Heart, Lung and Blood Institute

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