Controlling chronic hypertension in pregnancy

In women with hypertension only, superimposed preeclampsia is diagnosed when there is proteinuria of at least 500 mg in 24 hours or thrombocytopenia or abnormal liver enzymes (TABLE 3).

In women with hypertension and proteinuria (renal disease or class F diabetes), new onset of persistent symptoms (severe headache, visual changes) and/or thrombocytopenia, and/or elevated liver enzymes makes the diagnosis of preeclampsia.

Risk of abruption and other complications

Gravidas with chronic hypertension also have an increased risk for abruptio placentae.

In addition, women with high-risk chronic hypertension are at increased risk for life-threatening maternal complications such as pulmonary edema, hypertensive encephalopathy, retinopathy, cerebral hemorrhage, and acute renal failure.⁵ These risks are particularly acute in women with uncontrolled severe hypertension, renal dysfunction early in pregnancy, or left ventricular dysfunction prior to conception. The risk of these and other complications increases further when superimposed preeclampsia develops (TABLE 4).

Fetal and neonatal complications in women with chronic hypertension are 3 to 4 times more likely than in the general obstetric population.¹ These complications include premature delivery and small-for-gestational-age infants (TABLE 5).

Benefits vs risks of drug treatment

Although long-term blood pressure control greatly reduces stroke, cardiovascular morbidity, and mortality in nonpregnant persons,³ hypertension in pregnancy is different because the duration of therapy is shorter. In people with mild to moderate hypertension, the benefit is achieved after at least 5 years of treatment.² In pregnancy, the benefits to the mother may not be obvious during the short time of treatment, and exposure to drugs includes both mother and fetus.⁶ Thus, in pregnancy, one must balance the potential short-term maternal benefits against possible short- and long-term benefits and risks to the fetus and infant.^1,5,6

Low-risk: No benefit

We lack compelling evidence that shortterm antihypertensive therapy is beneficial in these women except for a reduction in the exacerbation of hypertension.^5,7

High-risk: Drug therapy is needed

We lack placebo-controlled trials of antihypertensive therapy in gravidas with severe hypertension, and none are likely to be performed because of the potential risks of untreated severe hypertension.

In these women, drug therapy reduces the acute risk of stroke, congestive heart failure, and renal failure.² Control of severe hypertension may also prolong the pregnancy and thereby improve perinatal outcome. However, there is no evidence that control of severe hypertension reduces the rates of superimposed preeclampsia or abruptio placentae.^2,4,5

Adverse effects

The potential adverse effects of the most commonly prescribed antihypertensive agents are poorly established or unclearly quantified.1 In general, we have limited and selective information about teratogenicity except in laboratory animals, and minimal data on the benefits and risks of most antihypertensive drugs when used during pregnancy. Nevertheless, the limited data available suggest that some drugs carry the potential for adverse fetal effects and should be avoided (TABLE 6).

Chronic hypertension heightens risk of placental abruption

Gravidas with chronic hypertension are at increased risk for abruptio placentae, which ranges from 0.7% to 1.5% in women with mild chronic hypertension, and from 5% to 10% in women with severe or high-risk hypertension. The rate increases to 30% with superimposed preeclampsia.

Drug treatment of comorbidities

According to data from clinical trials in nonpregnant subjects, selected comorbidities can be treated as follows:

• Ischemic heart disease. Beta-blockers are the first line of treatment, particularly labetalol. Alternatively, calciumchannel blockers can be used.
• Heart failure. In asymptomatic gravidas, beta-blockers should be used. In symptomatic gravidas, both beta-blockers and diuretics are recommended.
• Diabetes. Two or more drugs are usually needed to control blood pressure in this population. Although angiotensin-converting enzyme (ACE) inhibitors have a beneficial effect outside of pregnancy, calcium-channel blockers and diuretics are safer for gravidas.
• Chronic kidney disease warrants aggressive management, typically with 3 or more medications. Again, while ACE inhibitors have a favorable effect outside of pregnancy, calcium-channel blockers, beta-blockers, and diuretics are better choices.

ACE inhibitors are contraindicated in pregnancy due to the risk of oligohydramnios, renal dysplasia, pulmonary hypoplasia, and intrauterine growth restriction.⁸

Management goals

The primary objectives in managing chronic hypertension in pregnancy are to reduce maternal risks and achieve optimal perinatal survival. These objectives call for a rational approach that includes:

• preconception education and counseling,
• early antenatal care,
• frequent antepartum visits to monitor both mother and fetus,
• timely delivery with intensive intrapartum monitoring, and
• proper postpartum care.

Ideally, management should begin prior to pregnancy, with extensive evaluation and a complete workup to assess the cause and severity of the hypertension, determine whether other medical illnesses are present, and rule out target organ damage associated with longstanding hypertension (TABLE 7).

TABLE 2

Characteristics that affect risk of preeclampsia