Report of the Canadian Hypertension Society Consensus Conference: 3. Pharmacologic treatment of hypertensive disorders in pregnancy.

OBJECTIVE: To provide Canadian physicians with evidence-based guidelines for the pharmacologic treatment of hypertensive disorders in pregnancy. OPTIONS: No medication, or treatment with antihypertensive or anticonvulsant drugs. OUTCOMES: Prevention of maternal complications, and prevention of perinatal complications and death. EVIDENCE: Pertinent articles published from 1962 to September 1996 retrieved from the Pregnancy and Childbirth Module of the Cochrane Database of Systematic Reviews and from MEDLINE; additional articles retrieved through a manual search of bibliographies; and expert opinion. Recommendations were graded according to levels of evidence. VALUES: Maternal and fetal well-being were equally valued, with the belief that treatment side effects should be minimized. BENEFITS, HARMS AND COSTS: Reduction in the rate of adverse perinatal outcomes, including death. Potential side effects of antihypertensive drugs include placental hypoperfusion, intrauterine growth retardation and long-term effects on the infant. RECOMMENDATIONS: A systolic blood pressure greater than 169 mm Hg or a diastolic pressure greater than 109 mm Hg in a pregnant woman should be considered an emergency and pharmacologic treatment with hydralazine, labetalol or nifedipine started. Otherwise, the thresholds at which to start antihypertensive treatment are a systolic pressure of 140 mm Hg or a diastolic pressure of 90 mm Hg in women with gestational hypertension without proteinuria or pre-existing hypertension before 28 weeks' gestation, those with gestational hypertension and proteinuria or symptoms at any time during the pregnancy, those with pre-existing hypertension and underlying conditions or target-organ damage, and those with pre-existing hypertension and superimposed gestational hypertension. The thresholds in other circumstances are a systolic pressure of 150 mm Hg or a diastolic pressure of 95 mm Hg. For nonsevere hypertension, methyldopa is the first-line drug; labetalol, pindolol, oxprenolol and nifedipine are second-line drugs. Fetal distress attributed to placental hypoperfusion is rare, and long-term effects on the infant are unknown. Magnesium sulfate is recommended for the prevention and treatment of seizures. VALIDATION: The guidelines are more precise but compatible with those from the US and Australia.