What is Pregnancy-Induced Hypertension (PIH) and how is it managed in a pregnant female?

Pregnancy-Induced Hypertension (PIH): Comprehensive Overview

Definition and Classification

Pregnancy-induced hypertension is defined as new-onset hypertension (BP ≥140/90 mmHg) developing after 20 weeks of gestation in a previously normotensive woman, without significant proteinuria, and typically resolving within 42 days postpartum. 1, 2

Diagnostic Criteria

• Blood pressure threshold: Systolic BP ≥140 mmHg OR diastolic BP ≥90 mmHg on at least two separate occasions 1
• Timing: Must develop after 20 weeks of gestation 3, 1
• Absence of proteinuria: Distinguishes gestational hypertension from preeclampsia (proteinuria <0.3 g/day) 3

Severity Classification

• Mild hypertension: 140-159/90-109 mmHg 3, 1
• Severe hypertension: ≥160/110 mmHg (hypertensive emergency requiring immediate hospitalization) 3, 1, 2

Four Categories of Hypertension in Pregnancy

PIH encompasses four distinct clinical entities 3, 1:

1. Pre-existing (chronic) hypertension: BP ≥140/90 mmHg that precedes pregnancy or develops before 20 weeks gestation, persisting >42 days postpartum 3

2. Gestational hypertension: New-onset hypertension after 20 weeks without proteinuria, complicating 6-7% of pregnancies 3, 2

3. Pre-eclampsia: Gestational hypertension with clinically significant proteinuria (≥0.3 g/day or ≥30 mg/mmol urinary creatinine) 3

4. Pre-existing hypertension with superimposed gestational hypertension and proteinuria: Worsening BP and protein excretion ≥3 g/day after 20 weeks in women with chronic hypertension 3

Epidemiology and Clinical Significance

• Incidence: Complicates 6-10% of pregnancies 3, 2, 4
• Progression risk: Approximately 20-25% of women with gestational hypertension progress to preeclampsia 1, 2
• Maternal risks: Abruptio placentae, cerebrovascular events (stroke), organ failure, disseminated intravascular coagulation, and death 4
• Fetal/neonatal risks: Intrauterine growth restriction, prematurity (accounts for 25% of infants with very low birth weight <1500g), intrauterine death, and neonatal hematological disorders 3, 4, 5

Management Algorithm

Initial Assessment and Monitoring

For all women with suspected PIH, obtain baseline measurements including 2:

• Blood pressure readings on at least two separate occasions
• 24-hour ambulatory BP monitoring (superior to conventional measurements for predicting proteinuria, preterm delivery, and pregnancy outcomes) 1
• Urinalysis for proteinuria (24-hour urine collection or spot urine protein-to-creatinine ratio) 3, 2
• Baseline laboratory assessment: complete blood count (platelets), liver enzymes, renal function, uric acid 2
• Fetal assessment: ultrasound for growth, antenatal testing for fetal well-being 2

Non-Pharmacological Management

For mild hypertension (140-150/90-99 mmHg), initiate non-pharmacological approach first 3, 2:

• Close supervision with frequent BP monitoring (consider home BP monitoring) 1, 2
• Activity limitation and possible short-term hospitalization 3, 2
• Normal diet without salt restriction 3
• Avoid weight reduction during pregnancy (associated with reduced neonatal weight) 3

Common pitfall: Do not assume gestational hypertension is benign—20% progress to preeclampsia and require enhanced monitoring throughout pregnancy and postpartum 1

Pharmacological Management

Treatment Thresholds

Initiate antihypertensive medication at BP ≥140/90 mmHg in women with 2, 4:

• Gestational hypertension with or without proteinuria
• Pre-existing hypertension with superimposed gestational hypertension
• Hypertension with asymptomatic organ damage or symptoms at any time during pregnancy

Target blood pressure: Systolic BP 110-140 mmHg and diastolic BP 85-90 mmHg 2

First-Line Antihypertensive Agents

Methyldopa, labetalol, and long-acting nifedipine are equally acceptable first-line options 3, 2, 4:

• Methyldopa: Drug of choice with longest safety record (7.5-year infant follow-up data available); use with caution in women at risk for postpartum depression 3, 4
• Labetalol: Efficacy comparable to methyldopa; can be given IV for severe hypertension 3, 2, 4
• Long-acting nifedipine: Equally effective alternative 3, 2
• Metoprolol: Also recommended, though atenolol should be used with caution due to association with fetal growth retardation when used long-term 3, 4

Strictly Contraindicated Medications

ACE inhibitors, ARBs, and direct renin inhibitors are absolutely contraindicated in pregnancy due to severe fetotoxicity, particularly in second and third trimesters 3, 4. If taken inadvertently in first trimester, switch immediately to alternative medication and perform close fetal ultrasound monitoring 3

Management of Severe Hypertension (≥160/110 mmHg)

Severe hypertension is a hypertensive emergency requiring immediate hospitalization and urgent treatment within 15 minutes 3, 2:

Immediate Treatment Goals

• Decrease mean BP by 15-25% 2
• Target systolic BP 140-150 mmHg and diastolic BP 90-100 mmHg 2

Emergency Medications

• IV labetalol: Preferred first-line agent 3, 2
• Oral methyldopa or oral long-acting nifedipine: Alternative options 3
• IV sodium nitroprusside: Treatment of choice for hypertensive crises, but prolonged use carries risk of fetal cyanide poisoning (metabolized to thiocyanate) 3
• IV nitroglycerin: Drug of choice for preeclampsia with pulmonary edema 3

Important caveat: IV hydralazine should no longer be used as it is associated with more perinatal adverse effects than other drugs 3

Severe Preeclampsia Warning Signs

Monitor closely for symptoms requiring immediate intervention 3:

• Right upper quadrant or epigastric pain (liver edema and hepatic hemorrhage)
• Headache and visual disturbances (cerebral edema)
• Occipital lobe blindness
• Hyperreflexia and clonus
• Convulsions (eclampsia)
• HELLP syndrome (hemolysis, elevated liver enzymes, low platelet count)

Delivery Planning

• Stable gestational hypertension: Plan delivery at 37 weeks and 0 days 2
• Preeclampsia with severe features: Deliver promptly regardless of gestational age after immediate stabilization 2

Postpartum Management

The postpartum period is critical—10% of maternal deaths from hypertensive disorders occur postpartum, including stroke and eclampsia 1:

Monitoring Schedule

• BP recorded shortly after birth 2
• Follow-up at 48-72 hours postpartum 2
• Follow-up at 7-14 days postpartum 2
• Follow-up at 6 weeks postpartum 2
• Reassessment at 42 days postpartum to determine if hypertension persists (if so, reclassify as chronic hypertension) 3, 1

Long-Term Cardiovascular Risk

All women with gestational hypertension or preeclampsia require annual medical review lifelong due to significantly increased lifetime cardiovascular risk 2. These women have higher rates of future chronic hypertension and cardiovascular disease 2.

Key Clinical Pitfalls to Avoid

1. Masking of pre-existing hypertension: Physiological BP fall in first trimester may mask chronic hypertension, which appears later as "gestational" hypertension 3

2. Underestimating progression risk: 20-25% of gestational hypertension cases progress to preeclampsia—never assume it is benign 1, 2

3. Inadequate postpartum monitoring: Complications can worsen or initially present after delivery 1

4. Using contraindicated medications: Never use ACE inhibitors, ARBs, or direct renin inhibitors in pregnancy 3, 4

5. Delaying treatment of severe hypertension: BP ≥160/110 mmHg requires treatment within 15 minutes to prevent maternal stroke 2

6. Aggressive BP lowering: Excessively low BP may impair uteroplacental perfusion and jeopardize fetal development—target 110-140/85-90 mmHg 3, 2