Hypertension Treatment in Pregnancy

Hypertension in pregnancy is a pressure of 140/90 mmHg or over and includes chronic hypertension, gestational hypertension and pre-eclampsia. Treatment protects the mother from stroke and severe hypertension but does not cure pre-eclampsia. Severe hypertension, 160/110 mmHg or over, is an emergency that needs treatment within 30 to 60 minutes. Aim to keep pressure at 110 to 135/85 mmHg once treated, avoiding sharp falls that reduce placental flow.

Stop before conception or on confirmation. ACE inhibitors, angiotensin receptor blockers, spironolactone and renin inhibitors cause foetal kidney injury and malformation. Stop them and switch.

Prevention. In women at high risk of pre-eclampsia, give aspirin 150 mg orally at night from 12 weeks until 36 weeks. Where dietary calcium intake is low, give calcium 1.5 to 2 g orally daily.

First line. Labetalol 100 to 200 mg orally twice daily, increased every 2 to 3 days to a maximum of 2.4 g daily in two to four doses. Avoid in asthma and in hepatic impairment.

Alternative. Nifedipine modified-release 10 to 20 mg orally twice daily, maximum 60 mg twice daily (120 mg daily).

Methyldopa. 250 mg orally two or three times daily, maximum 3 g daily (usually 2 g). Often available where other drugs are not. Avoid in depression, and stop within 2 days of birth.

Avoid. ACE inhibitors, angiotensin receptor blockers, spironolactone, atenolol and, unless essential, new thiazides.

Severe hypertension, 160/110 mmHg or over.

• Labetalol 20 mg intravenously over 2 minutes, then 40 mg, then 80 mg at 10 minute intervals, to a total of 220 mg, or an infusion at 1 to 2 mg/min.
• Nifedipine immediate-release 10 mg orally, repeated at 20 to 30 minutes, then 20 mg, to a maximum of 50 mg.
• Hydralazine 5 mg intravenously, repeated at 20 minute intervals with 5 to 10 mg, to a maximum of 20 mg.

Seizure prevention. In severe pre-eclampsia give magnesium sulphate 4 g intravenously over 5 to 15 minutes, then 1 g/hour for 24 hours. Check reflexes, respiratory rate over 12 breaths a minute and urine output over 30 mL/hour. Antidote for toxicity is calcium gluconate 1 g intravenously over 10 minutes. Reduce the infusion in renal impairment.

Breastfeeding. Labetalol, nifedipine, methyldopa, enalapril and captopril are compatible. Pressure peaks 3 to 6 days after birth, so continue treatment.

Monitoring. Pressure at every visit, urine protein, platelets, creatinine and liver enzymes in pre-eclampsia, and foetal growth and wellbeing. During magnesium treatment, observe continuously.

Renal and hepatic. Reduce the magnesium maintenance dose when creatinine clearance is under 30 mL/min. Avoid labetalol in significant hepatic disease.

Targets after birth. Treat to under 150/100 mmHg and review within 3 to 5 days.

Stopping. Taper treatment postnatally as pressure falls. Restart an ACE inhibitor after birth when chronic hypertension or kidney disease needs it, since enalapril is compatible with breastfeeding.

Common errors. Continuing an ACE inhibitor in the first trimester without counselling, lowering pressure under 110/80 mmHg, and giving magnesium without monitoring.

Referral and escalation. Refer urgently for 160/110 mmHg or over, headache or visual symptoms, epigastric pain, platelets under 100 x 10^9/L, abnormal liver enzymes, eclampsia, or foetal compromise.