One unhappy effect of the obesity epidemic and the increasing age of women at childbirth is the rising prevalence of chronic hypertension, which climbed from 4.6% to 22.3% in women aged 30 to 39 years, and from 0.6% to 2.0% in women aged 18 to 29 years, according to the National Health and Nutrition Examination Survey for 1988–1991. These trends are expected to continue, and so are the rates of chronic hypertension in pregnancy, with its increased possibility of super-imposed preeclampsia.
This article outlines diagnosis and management, including:
- how to tell when drug therapy is needed
- how to detect superimposed preeclampsia
- when to discontinue drug regimens
- which drugs and doses should be used during pregnancy and after delivery.
When is hypertension “chronic”?
Hypertension is chronic if the elevated blood pressure was documented before pregnancy. If prepregnancy blood pressure is unknown, the patient is thought to have chronic hypertension if it is consistently elevated before 20 weeks of gestation.
Blood pressure is elevated if systolic pressure is at least 140 mm Hg or diastolic pressure is at least 90 mm Hg. These blood pressure ranges should be documented on at least 2 occasions at least 4 hours apart.1
Diagnosis may be difficult in women with previously undiagnosed chronic hypertension who begin prenatal care after 16 weeks’ gestation, because a physiologic decrease in blood pressure usually begins at that time. These women are more likely to be erroneously diagnosed as having gestational hypertension.2
Chronic hypertension is primary (essential) in approximately 80% to 90% of cases, and, in 10% to 20% of cases, secondary to collagen vascular disease, or renal, endocrine, or vascular disorders.
Outside of pregnancy, hypertension is categorized into 3 stages: prehypertension, stage 1 hypertension, and stage 2 hypertension.3
Mild vs severe, low-risk vs high-risk
During pregnancy, chronic hypertension is classified according to its severity, depending on the systolic and diastolic blood pressures. Systolic pressures of at least 160 mm Hg and/or diastolic pressures of at least 110 mm Hg constitute severe hypertension (Korotkoff phase V). The diagnosis requires documented evidence of hypertension before pregnancy and/or before 20 weeks’ gestation.
Korotkoff phase V readings are more precise. This phase occurs when the sound disappears, as opposed to phase IV, in which the sound is muffled. Phase V is more accurate because it correlates with actual intra-arterial pressure. Moreover, phase IV cannot be recorded in at least 10% of gravidas because of hemodynamic changes of pregnancy.
Low vs high risk. For management and counseling purposes, chronic hypertension in pregnancy also is classified as low- or high-risk (TABLE 1). A gravida has a low risk when she has mild essential hypertension without any organ involvement.
Blood pressure criteria are based on measurements at the initial visit regardless of whether the patient is taking antihypertensive drugs. For example, if the patient has blood pressure of 140/80 mm Hg and is taking antihypertensive agents, she is nevertheless classified as low-risk. Her medications are discontinued, and blood pressure is monitored very closely. If readings reach severe levels, she is then classified as high-risk and managed as such.
Risk classification may change. A woman initially classified as low-risk early in pregnancy may become high-risk if preeclampsia or severe hypertension develops.
Low- and high-risk criteria
|LOW RISK||HIGH RISK|
|Uncomplicated essential hypertension||Secondary hypertension|
|Target organ damage*|
|No previous perinatal loss||Previous perinatal loss|
|Systolic pressure <160 mm Hg and diastolic pressure <110 mm Hg||Maternal age >40 years|
|Systolic pressure ≥160 mm Hg or diastolic pressure ≥110 mm Hg|
|*Left ventricular dysfunction, retinopathy, dyslipidemia, microvascular disease, or stroke.|
Risk factors for preeclampsia
Pregnancies complicated by chronic hypertension carry a heightened risk of superimposed preeclampsia, which is associated with high rates of adverse maternal and perinatal outcomes.4 Sibai and colleagues4 documented the rate of superimposed preeclampsia among 763 women with chronic hypertension who were followed prospectively at several medical centers in the United States. The overall rate of superimposed preeclampsia was 25%.
Specific characteristics affected the risk of preeclampsia: age, previous preeclampsia, duration of hypertension, diastolic blood pressure, thrombophilia, diabetes, proteinuria, multifetal gestation, and use of assisted reproductive technology (TABLE 2).