Management of Hypertension in Pregnancy

Classification

1. Blood Pressure Thresholds for Treatment

• Severe HTN (SBP ≥160 or DBP ≥105–110 mmHg): antihypertensive therapy is clearly indicated to prevent stroke and cardiovascular complications.
• Mild-to-moderate HTN: evidence less clear. The CHIPS trial (Control of Hypertension in Pregnancy Study) demonstrated that targeting a "tight" DBP of 85 mmHg (vs. a "less-tight" DBP of 100 mmHg) significantly reduced maternal complications including severe hypertension, thrombocytopenia, and transaminitis — with no difference in fetal/neonatal outcomes (pregnancy loss, need for high-level neonatal care, SGA rates).

Current recommendation: Treat to a target DBP of ~85 mmHg. Aggressive BP lowering should be avoided as it can cause fetal distress, particularly when placental perfusion is already compromised.

2. Antihypertensive Drug Selection

Safe agents in pregnancy:

Contraindicated in pregnancy:

ACEi/ARBs must be stopped immediately on confirmation of pregnancy. Eplerenone appears a safer alternative to spironolactone when mineralocorticoid antagonism is needed.

3. Management of Preeclampsia

Timing of Delivery

• <24 weeks: Delivery usually recommended (perinatal mortality >80% even with expectant management)
• >37 weeks: Immediate delivery almost always indicated
• 24–37 weeks: Balance neonatal benefit of prolonging pregnancy against maternal risk; expedite if:
  • Non-reassuring fetal testing
  • Suspected abruption
  • Thrombocytopenia
  • Worsening renal/liver function
  • Unrelenting headache, visual changes, epigastric pain

Magnesium Sulfate — Seizure Prophylaxis

• Magnesium is the drug of choice for prevention and treatment of eclamptic seizures.
• The Magpie Trial (>10,000 women, 33 countries) showed MgSO₄ reduced eclamptic seizure incidence by 50% (0.8% vs. 1.9% with placebo).
• Superior to diazepam and phenytoin (shown in two earlier RCTs, 1995).
• Used for prophylaxis in severe preeclampsia and treatment of eclampsia.
• Typical regimen: 4–6 g IV loading dose → 1–2 g/hr maintenance infusion.
• Monitor for toxicity: loss of patellar reflexes (first sign), respiratory depression, cardiac arrest (at very high levels). Antidote: calcium gluconate 1 g IV.

4. Chronic Hypertension in Pregnancy — Special Considerations

• Pre-pregnancy: optimise BP using pregnancy-safe agents; counsel about risks (preeclampsia, preterm birth, IUGR).
• Screen for secondary causes (affects at least 10% of women with chronic HTN in pregnancy): renal artery stenosis, primary hyperaldosteronism, OSA, phaeochromocytoma. Note: standard screening tests (e.g., aldosterone-renin ratio) are not validated in pregnancy; CT/angiography relatively contraindicated.
• OSA: found in ~40% of pregnant women with HTN; screen high-risk women (obesity, snoring).
• Phaeochromocytoma: rare but catastrophic if undiagnosed — hypertensive crisis can be triggered by labour; surgical intervention usually postponed until after delivery.
• Mineralocorticoid receptor mutation (rare): progesterone activates the mutant receptor → severe HTN exacerbation in pregnancy without preeclampsia features.

5. HELLP Syndrome

Summary: Key Points

1. Treat severe HTN (≥160/105–110 mmHg) promptly — labetalol IV or nifedipine oral are first-line for acute management.
2. For non-severe HTN, target DBP ~85 mmHg (CHIPS trial evidence).
3. Stop ACEi/ARBs immediately in pregnancy.
4. Methyldopa, labetalol, and nifedipine are the backbone of oral chronic therapy.
5. MgSO₄ is mandatory for seizure prophylaxis/treatment in preeclampsia/eclampsia.
6. Delivery is the definitive treatment — timing depends on gestational age and clinical severity.