What is the definition and management of gestational hypertension based on mean arterial pressure (MAP)?

Gestational Hypertension Definition and Management Based on Mean Arterial Pressure

Gestational hypertension is defined as pregnancy-induced hypertension without proteinuria, diagnosed by absolute blood pressure values ≥140/90 mmHg that develops after 20 weeks of gestation and typically resolves within 42 days postpartum. 1

Definition and Classification

Diagnostic Criteria

• Blood pressure threshold: ≥140 mmHg systolic or ≥90 mmHg diastolic
• Timing: Develops after 20 weeks of gestation
• Resolution: Usually resolves within 42 days postpartum
• Absence of proteinuria: Distinguished from preeclampsia
• Diagnosis requires at least two elevated blood pressure readings on separate occasions

While Mean Arterial Pressure (MAP) is not specifically used in the standard definition of gestational hypertension according to major guidelines, it can be calculated as:

• MAP = [(2 × Diastolic BP) + Systolic BP] ÷ 3

Classification of Hypertensive Disorders in Pregnancy

1. Pre-existing hypertension (1-5% of pregnancies)
2. Gestational hypertension (6-7% of pregnancies)
3. Pre-existing hypertension with superimposed gestational hypertension with proteinuria
4. Antenatally unclassifiable hypertension

Management Based on Blood Pressure Severity

Mild Hypertension (140-159/90-109 mmHg)

• Non-pharmacological management is recommended initially:
  • Close supervision
  • Limitation of activities
  • Normal diet without salt restriction
  • Regular monitoring of maternal and fetal condition

Severe Hypertension (≥160/110 mmHg)

• Considered a medical emergency requiring hospitalization
• Pharmacological intervention is necessary:
  • First-line medications: IV labetalol, oral methyldopa, or oral nifedipine
  • Avoid IV hydralazine due to increased perinatal adverse effects 1
  • IV sodium nitroprusside for hypertensive crises (with caution due to risk of fetal cyanide poisoning)
  • Nitroglycerin for pre-eclampsia with pulmonary edema

Monitoring Considerations

• 24-hour ambulatory blood pressure monitoring is superior to conventional measurements for:

  • Predicting proteinuria
  • Assessing risk of pre-term delivery
  • Predicting infant birth weight
  • Evaluating overall pregnancy outcomes 1

• Particularly useful in high-risk pregnant women with:

  • Pre-existing hypertension
  • Diabetes
  • Renal damage

Medication Selection

For non-severe hypertension requiring pharmacological management:

• Methyldopa (drug of choice in pregnancy)
• Labetalol (efficacy comparable to methyldopa)
• Calcium antagonists (nifedipine)
• Atenolol should be used with caution due to risk of fetal growth restriction 1, 2

Important Considerations and Pitfalls

1. Contraindicated medications: ACE inhibitors, ARBs, and direct renin inhibitors are strictly contraindicated due to severe fetotoxicity 1

2. Blood pressure fluctuations: Normal BP typically falls in the second trimester (approximately 15 mmHg lower than pre-pregnancy) and returns to or exceeds pre-pregnancy levels in the third trimester 1

3. Measurement technique: Korotkoff phase V (disappearance of sound) is recommended for diastolic BP measurement, with phase IV only used if sounds persist at near-zero cuff pressures 1

4. Progression risk: Women with gestational hypertension should be monitored closely for progression to preeclampsia, which occurs when significant proteinuria develops (≥0.3 g/day or ≥30 mg/mmol urinary creatinine) 1

5. Hemodynamic considerations: Recent research suggests gestational hypertension and preeclampsia have different hemodynamic profiles, with preeclampsia involving venous hemodynamic dysfunction 3

6. Neonatal outcomes: Increasing mean arterial pressure is associated with adverse neonatal outcomes including NICU admission, low birth weight, and small for gestational age infants 4

While the 24-hour mean of blood pressure has limitations as a standalone screening test for gestational hypertension 5, it remains a valuable component of comprehensive assessment, especially when combined with other clinical parameters.