How should late‑onset pregnancy‑induced hypertension (onset after 34 weeks gestation with no significant proteinuria) be managed?

Management of Late-Onset Pregnancy-Induced Hypertension

Initial Assessment and Blood Pressure Management

Women with late-onset pregnancy-induced hypertension (onset after 34 weeks without significant proteinuria) should be treated with antihypertensive medication when blood pressure is consistently ≥140/90 mmHg, targeting a diastolic BP of 85 mmHg and systolic BP of 110-140 mmHg, with delivery planned at 37-38 weeks gestation. 1, 2

Blood Pressure Thresholds and Treatment Initiation

• Initiate antihypertensive treatment when BP is consistently ≥140/90 mmHg in clinic/office (or ≥135/85 mmHg at home) to reduce the likelihood of developing severe maternal hypertension and complications such as low platelets and elevated liver enzymes. 1

• Severe hypertension (≥160/110 mmHg) requires urgent treatment within 30-60 minutes in a monitored setting to prevent maternal stroke or cerebral hemorrhage. 1, 2

• For urgent treatment of severe hypertension, use oral nifedipine or intravenous labetalol or hydralazine as first-line agents; oral labetalol may be used if these are unavailable. 1

Maintenance Antihypertensive Therapy

For non-severe but persistent hypertension (140-159/90-109 mmHg), acceptable oral agents include:

• Methyldopa (drug of choice in pregnancy) 3, 4
• Labetalol (efficacy comparable to methyldopa) 1, 3, 4
• Nifedipine (long-acting formulation) 1, 4
• Oxprenolol 1

Second or third-line agents include hydralazine and prazosin. 1

Reduce or cease antihypertensive drugs if diastolic BP falls below 80 mmHg. 1

Critical Monitoring Protocol

Maternal Assessment

Women should be assessed in hospital when first diagnosed; thereafter, some may be managed as outpatients once their condition is stable and they can reliably report problems and monitor their BP. 1

Monitor for progression to preeclampsia by assessing for:

• New-onset proteinuria using automated dipstick urinalysis; if positive, quantify with urine protein/creatinine ratio (≥30 mg/mmol is abnormal). 1, 5

• Blood pressure measurements at least twice weekly or more frequently if clinical deterioration occurs. 5

• Clinical assessment including evaluation for clonus, severe headache, visual disturbances, and epigastric/right upper quadrant pain. 1, 2

• Laboratory tests at least twice weekly: hemoglobin, platelet count, liver transaminases (AST/ALT), creatinine, and uric acid. 1, 2

Fetal Surveillance

Perform initial ultrasound assessment at diagnosis to confirm fetal well-being, including:

• Fetal biometry 1, 2
• Amniotic fluid volume 1, 2
• Umbilical artery Doppler 1, 2

Repeat ultrasound every 2 weeks if initial assessment is normal; more frequently if fetal growth restriction is present. 2

Delivery Timing

Deliver at 37 weeks and zero days gestation or beyond, regardless of whether proteinuria develops or blood pressure remains controlled. 1, 5

Deliver immediately after maternal stabilization if any of the following develop at any gestational age:

• Repeated episodes of severe hypertension despite maintenance treatment with 3 classes of antihypertensive agents 1, 2
• Progressive thrombocytopenia (declining platelet counts on serial measurements) 1, 2
• Progressively abnormal renal or liver enzyme tests (worsening trends, not static elevations) 1, 2
• Pulmonary edema 1, 2
• Abnormal neurological features: severe intractable headache, repeated visual scotomata, or convulsions 1, 2
• Non-reassuring fetal status 1, 2
• Maternal oxygen saturation deterioration (<90%) 2

Vaginal delivery is preferred unless cesarean is indicated for standard obstetric reasons. 1, 2

Magnesium Sulfate for Seizure Prophylaxis

Administer magnesium sulfate if the patient develops proteinuria with severe hypertension or any neurological signs/symptoms:

• Loading dose: 4-5g IV over 5 minutes 1, 2
• Maintenance: 1-2g/hour continuous IV infusion 1, 2

Monitor hourly urine output via Foley catheter (target ≥100 mL/4 hours), deep tendon reflexes before each dose, and respiratory rate to detect magnesium toxicity. 2

Critical Pitfalls to Avoid

• Do not underestimate disease severity based on absence of proteinuria—approximately 25% of gestational hypertension cases progress to preeclampsia, and serious organ dysfunction can develop at relatively mild hypertension levels. 2, 6

• Do not delay delivery at ≥37 weeks based on well-controlled blood pressure—gestational age ≥37 weeks is an absolute indication for delivery regardless of BP control or fetal testing results. 1, 2, 5

• Do not use ACE inhibitors, ARBs, or direct renin inhibitors—these are absolutely contraindicated due to severe fetotoxicity. 2, 3

• Do not use diuretics routinely—they further reduce plasma volume, which is already contracted in hypertensive disorders of pregnancy. 2, 5

• Do not use short-acting oral nifedipine, especially when combined with magnesium sulfate, due to risk of uncontrolled hypotension and fetal compromise. 2

Postpartum Management

Continue antihypertensive medications administered antenatally and monitor BP at least every 4 hours while awake for a minimum of 3 days postpartum, as hypertension can worsen between days 3-6 after delivery. 2, 5

Replace methyldopa with an alternative antihypertensive agent postpartum if it was used during pregnancy, particularly in women at risk of depression. 1, 2

Review all women at 6 weeks postpartum to ensure BP and proteinuria have normalized; refer for further investigation if abnormalities persist. 1, 5

Counsel women that a history of pregnancy-induced hypertension confers significant long-term cardiovascular risk requiring annual medical review lifelong. 5, 4