Pre-existing hypertension during pregnancy, also known as chronic hypertension, refers to elevated blood pressure diagnosed before pregnancy or before 20 weeks of gestation. This condition significantly influences maternal and fetal outcomes and requires vigilant monitoring, targeted therapy, and multidisciplinary care.
Classification and Diagnostic Criteria
Pre-existing hypertension is classified by the American College of Obstetricians and Gynecologists (ACOG) as systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg present before pregnancy or prior to 20 weeks gestation. It may present as:
- Essential (Primary) Hypertension: No identifiable cause
- Secondary Hypertension: Resulting from renal, endocrine, or vascular disorders
Diagnostic Criteria
| Category | Systolic BP | Diastolic BP |
|---|---|---|
| Mild Hypertension | 140–159 mmHg | 90–109 mmHg |
| Severe Hypertension | ≥160 mmHg | ≥110 mmHg |
Blood pressure must be confirmed on at least two occasions, four hours apart, using validated measurement techniques.
Pathophysiology and Maternal Adaptation
The physiologic cardiovascular adaptations of pregnancy—such as increased plasma volume, cardiac output, and decreased systemic vascular resistance—can unmask or exacerbate chronic hypertension. These hemodynamic shifts are less well tolerated in patients with impaired vascular compliance or pre-existing endothelial dysfunction.
Maternal and Fetal Risks Associated with Chronic Hypertension
Maternal Risks
- Superimposed preeclampsia
- Placental abruption
- Cerebrovascular events
- Renal impairment
- Cardiomyopathy
Fetal Risks
- Intrauterine Growth Restriction (IUGR)
- Preterm delivery
- Stillbirth
- Neonatal Intensive Care Unit (NICU) admission
- Low birth weight
Timely detection and proactive management are essential to mitigate these outcomes.
Antenatal Management and Surveillance
Initial Evaluation
A comprehensive assessment includes:
- Baseline blood pressure profile
- Renal function tests (creatinine, urinalysis)
- Liver enzymes
- Electrocardiogram (ECG)
- Fundoscopy
- Assessment for end-organ damage
Ongoing Monitoring
| Parameter | Frequency |
|---|---|
| BP Monitoring | Every prenatal visit |
| Urinalysis | Monthly (more frequently if proteinuria suspected) |
| Ultrasound for Growth | Every 4 weeks after 24 weeks gestation |
| Non-stress Test / Biophysical Profile | Initiated from 32–34 weeks or earlier if IUGR suspected |
Pharmacologic Treatment in Pregnancy
Treatment is recommended if BP ≥160/110 mmHg, or 140/90 mmHg with end-organ involvement or additional comorbidities.
Safe Antihypertensive Agents
| Drug | Class | Notes |
|---|---|---|
| Labetalol | Beta-blocker | First-line agent; contraindicated in asthma |
| Methyldopa | Central alpha-agonist | Safe but less effective; used widely |
| Nifedipine (extended-release) | Calcium channel blocker | Effective; avoid short-acting form |
| Hydralazine | Vasodilator | Used acutely in hospital setting |
Contraindicated Agents
- ACE Inhibitors
- Angiotensin II Receptor Blockers (ARBs)
- Direct Renin Inhibitors
These drugs are teratogenic and associated with fetal renal failure, oligohydramnios, and death.
Management of Superimposed Preeclampsia
Superimposed preeclampsia occurs in women with chronic hypertension who develop new-onset proteinuria or other features of preeclampsia after 20 weeks. Management includes:
- Hospitalization for severe cases
- Magnesium sulfate for seizure prophylaxis
- Corticosteroids for fetal lung maturation if early delivery is anticipated
- Intensive fetal monitoring
Delivery is the definitive cure; timing is based on gestational age, maternal stability, and fetal status.
Timing and Mode of Delivery
Elective Delivery Recommendations
- Uncomplicated chronic hypertension: 38–39 weeks
- Superimposed preeclampsia: 34–37 weeks or earlier if unstable
- Uncontrolled BP or IUGR: Individualized, often before 37 weeks
Mode of Delivery
Vaginal delivery is preferred unless obstetric indications dictate otherwise. Cesarean section is reserved for fetal distress or failure to progress.
Postpartum Considerations
- Continue antihypertensives, adjusting doses postpartum
- Monitor for postpartum preeclampsia or eclampsia
- Encourage breastfeeding-compatible medications (e.g., labetalol, nifedipine)
- Educate on long-term cardiovascular risks
Long-Term Implications
Women with pre-existing hypertension face increased risk of:
- Chronic kidney disease
- Cardiovascular disease
- Recurrent hypertensive complications in future pregnancies
Postpartum counseling and lifestyle modifications are essential components of care.
Preventive Measures and Patient Counseling
- Preconception Planning: BP control, medication adjustments, folic acid supplementation
- Lifestyle Modifications: Sodium restriction, physical activity, weight management
- Aspirin Prophylaxis: Low-dose aspirin (81 mg) from 12 to 36 weeks to reduce risk of preeclampsia
- Close Follow-Up: Regular antenatal and postnatal care
Frequently Asked Questions:
What is considered pre-existing hypertension in pregnancy?
Hypertension diagnosed before pregnancy or before 20 weeks gestation.
Can women with chronic hypertension have a healthy pregnancy?
Yes, with proper management and monitoring, most can achieve favorable outcomes.
Which blood pressure medications are safe during pregnancy?
Labetalol, methyldopa, and nifedipine (extended-release) are considered safe.
What are the signs of superimposed preeclampsia?
New-onset proteinuria, elevated liver enzymes, thrombocytopenia, and worsening hypertension.
Is delivery always required early in hypertensive pregnancies?
Not always. Timing depends on blood pressure control and maternal-fetal well-being.
Effective management of pre-existing hypertension during pregnancy requires a structured approach that integrates accurate diagnosis, tailored pharmacologic therapy, and rigorous maternal-fetal surveillance. With comprehensive prenatal care, most women with chronic hypertension can experience healthy pregnancies and positive outcomes for both mother and child.
