• Severe hypertension is a systolic blood pressure (SBP) ≥160 mmHg or a diastolic blood pressure (DBP) ≥110 mmHg.
  
• Persistence of hypertension should be confirmed after at least 5–15 minutes of rest.

The definition of severe diastolic hypertension is quite consistently a DBP ≥110 mmHg. The definition of severe systolic hypertension varies between 160 and 170 mmHg or greater. Support for use of a SBP ≥160 mmHg is based on its association with an increased risk of stroke in pregnancy [4]. We favor use of this more conservative threshold for treatment. Consideration of the patient’s baseline blood pressure may also be important, as cerebral hemorrhage can occur at lower blood pressures, particularly if there has been a significant acute change from prior readings. A rise in systolic or diastolic blood pressure of >50 mmHg may be associated with stroke in pre-eclamptic patients even in the absence of severe hypertension [5].

These statements assume that proper BP measurement technique is being employed, including ensuring that the brachial artery is held at the level of the heart during measurement and that the appropriate cuff size is being used (see Chapter 5).

That severe hypertension should be persistent is an important clinical management point. By this we mean that the severe elevation of BP be confirmed by repeat measurement, in 5–15 minutes.

Treatment of severe hypertension is not without its risks, as discussed below.

• Patients with severe hypertension should undergo a brief assessment by history, physical and laboratory evaluation for evidence of acute target organ damage. Key features of this assessment are reviewed in Box 39.1.
  
• Severe hypertension that is not clearly secondary to pre-eclampsia should prompt consideration of secondary causes of hypertension. Secondary cause of hypertension and some suggestive features of each etiology are reviewed in Table 42.1.

• Persistent, severe hypertension should be treated with an antihypertensive agent.
  
• Whether or not there is maternal end-organ dysfunction will determine whether there is a hypertensive “urgency” or “emergency.”
  
• Blood pressure should be lowered to <160 mmHg systolic and <110 mmHg diastolic, but by no more than 25% over minutes to hours.

Persistent, severe hypertension should always be treated. This will usually be by administration of antihypertensive therapy. However, if other factors that may be contributing to the severe hypertension (such as pain) can be addressed (by epidural analgesia, for example), observation may be appropriate over minutes to an hour or so.

Hypertensive urgencies are those associated with severe hypertension but not end-organ dysfunction (such as pulmonary edema or eclampsia). Severe hypertension with end-organ dysfunction defines a hypertensive “emergency.” Whether or not visual disturbances or headache should be defined as end-organ dysfunction is not clear, but many clinicians would regard them as such. In the setting of pregnancy and especially after 20 weeks gestation, hypertensive urgencies likely require hospitalization for treatment and monitoring. Urgencies may be treated with oral agents, which have peak drug effects in 1–2 hours (e.g. labetalol). Hypertensive emergencies should be treated with parenteral agents (and an arterial line) aimed at lowering mean arterial BP by no more than 25% over minutes to hours, and then further lowering BP to 160/100 mmHg over subsequent hours. Parenteral agents may also be preferable for women in active labor in whom gastric emptying may be delayed.