Beta-blockers are relatively effective agents in controlling hypertension during pregnancy from the 16th week to about 1 week prior to labor. Although they have been used effectively in patients within 72 h before labor and during delivery, other agents are preferred during this period. Blood pressure control, if required, just prior to delivery is best achieved with the use of IV hydralazine.

Beta-blockers have advantages over methyldopa for prolonged treatment of chronic hypertension during the last trimester. These agents do not usually cause orthostatic hypotension, somnolence, or significant depression. Also, methyldopa must be taken two or three times daily as opposed to beta-blockers, which are given once daily. The most common beta-blockers used during pregnancy are labetalol, atenolol, and pindolol. Atenolol caused no fetal adverse effects in 120 pregnant women; neonates showed a minor incidence of transient bradycardia not requiring therapy, and a 1-year follow-up gave results similar to those observed with methyldopa, with no differences in development or growth indices (Reynolds et al. 1984). In another study, 4 years follow-up revealed all normal infants (Olofsson et al. 1986). Chronic atenolol therapy does not increase the incidence of neonatal respiratory distress syndrome. In one study, no child in the actively treated group required ventilation, as opposed to seven infants in the control group requiring ventilation for the respiratory distress syndrome (Rubin et al. 1983).

Other studies with atenolol have found significantly lower infant birth and placental weights compared with the nontreatment arm (Churchill and Beevers 1999), and the concern appears to be unique to atenolol used for long-term but not for short-term treatment.

Adverse effects of beta-blockers used during pregnancy include: fetal or neonatal bradycardia; premature or prolonged labor; delayed spontaneous breathing in the newborn, mainly observed with IV use; and rarely neonatal hypoglycemia. Intrauterine growth retardation is often mentioned with the use of atenolol, and low infant birth weight may occur with long-term treatment.

The dosages of metoprolol and pindolol are much lower than those advised by the respective manufacturers.

Hypertensive crises in pregnancy: labetalol IV infusion: 20 mg/h titrated slowly with continuous BP monitoring; the dose is doubled every 30 min if needed to 40 mg, maximum 160 mg/h . The combination with IV hydralazine allows lower doses of both agents with fewer side effects.

Labetalol is a beta-adrenergic blocking agent with alpha₁-blocking properties, and thus it causes vasodilation. The latter effect may result in orthostatic hypotension. The drug may also cause fatal or life-threatening hepatic necrosis. Labetalol is as effective as methyldopa in controlling hypertension during pregnancy. The drug is extremely useful in the acute short-term management of severe resistant hypertension just before labor or during delivery. Avoid in asthmatics. Some state that labetalol is generally safer and preferable to atenolol (Churchill and Beevers 1999).

Adverse effects include about a 27 % incidence of intrauterine growth retardation. The pregnant woman may experience perioral numbness, tingling, and itching of the scalp, and rarely a lupus-like illness, a lichenoid rash; a rare association is retroplacental hemorrhage (Lindheimer and Katz 1985). Also, a rare but life-threatening complication is acute hepatic necrosis (Clarke et al. 1990). These serious side effects are not caused by other beta-adrenergic blockers.

Labetalol use should be confined to hypertensive emergencies. The drug has a role given intravenously in the management of severe resistant hypertension (diastolic blood pressure >110 mmHg) associated with preeclampsia occurring just before or during delivery. Labetalol given intravenously appears to be more effective than IV hydralazine or methyldopa. The blood pressure-lowering effect is more predictable, and the drug causes less tachycardia and appears to cause less fetal distress than hydralazine.

For hypertensive crisis: IV bolus 5–10 mg.

Hydralazine is a pure arteriolar vasodilator and has been used extensively for acute control of severe hypertension in the third trimester of pregnancy.

The drug is teratogenic in animals. Safety for chronic use is not as secure as that observed with methyldopa or beta-blockers.

The drug causes reflex tachycardia and sodium and water retention, which may necessitate the use of a diuretic or a beta-blocker to blunt tachycardia as well as to enhance the antihypertensive effect.

The drug has a role in the short-term management of severe hypertension during late pregnancy unresponsive to methyldopa or beta-blockers. Acute lowering of blood pressure is necessary in severe preeclampsia to prevent cerebral hemorrhage, the main cause of the increase in maternal mortality seen in preeclampsia. The drug is very useful when a modest dose is combined with a low dose of a beta-blocking drug, such as atenolol 50 mg daily, or as an adjunct to methyldopa; combination therapy prevents tachycardia and headaches caused by hydralazine.

The chronic use of the drug is limited by adverse effects that include fetal thrombocytopenia, although this occurrence is rare. The mother may experience dizziness, postural hypotension, a lupus syndrome, palpitations, and edema.

Hydralazine is the mainstay of therapy for the treatment of acute severe hypertension (blood pressure >170/110 mmHg) occurring just before labor, during labor, or at delivery. Hydralazine remains the agent of choice, given as boluses (Patterson-Brown et al. 1994). The drug acts quickly and reduces blood pressure in a fairly well-controlled manner, although labetalol IV appears to be a reasonable alternative to hydralazine, producing a more predictable and controlled decrease in blood pressure. Also, nitroprusside is more effective but is contraindicated because of serious potential risks to the neonate. The drug does not decrease cardiac output and preserves uteroplacental blood flow.

Dosage: slow IV injection 5–10-mg bolus diluted with 10 mL 0.9 % sodium chloride given over 1–2 min, repeated in 20–30 min and then as often as necessary over several hours. The maximal effect of hydralazine is observed in 20 min. Duration of action is 6–8 h.

Hypertensive emergencies: Dosage: initially 200–300 micrograms/min; maintenance usually 50–150 micrograms/min, with continuous evaluation of heart rate and blood pressure and fetal monitoring. If hydralazine fails to control blood pressure adequately, the addition of methyldopa or labetalol is advisable. As indicated earlier, labetalol IV bolus or infusion appears to be a reasonable alternative for hydralazine-resistant hypertension. If nifedipine is chosen, caution is necessary not to give magnesium sulfate concomitantly because severe hypotension may ensue.

Because hypertension of pregnancy and preeclampsia are associated with reduced plasma volume, diuretics are not indicated. Fetal outcome is usually worse in women with preeclampsia who fail to expand plasma volume. Thiazides may cause neonatal thrombocytopenia, albeit rarely. Also, diuretics may exacerbate maternal carbohydrate intolerance. A meta-analysis of randomized trials involving more than 7,000 pregnant women indicated no increased incidence of adverse fetal effects (Collins et al. 1985). Other studies have shown fetal and neonatal jaundice as well as thrombocytopenia. (Furosemide is usually contraindicated during pregnancy; see later discussion of heart failure).