Hypertensive Disorders Of Pregnancy (HDP)

Introduction

Hypertensive disorders of pregnancy (HDP) are a leading cause of maternal and perinatal morbidity and mortality worldwide. For the MCCQE1, understanding the classification, diagnosis, and management of HDP according to SOGC (Society of Obstetricians and Gynaecologists of Canada) guidelines is essential.

This topic integrates several CanMEDS roles, particularly Medical Expert (diagnosis and management) and Health Advocate (recognizing long-term cardiovascular risks for women with HDP).

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Canadian Context: HDP affects approximately 7% of pregnancies in Canada. Indigenous women and those in remote communities often face higher risks due to barriers in accessing prenatal care.

Classification of Hypertensive Disorders

The SOGC classifies HDP into four main categories. Understanding the timing of onset and associated features is critical for the exam.

Pre-existing Hypertension

Defined as hypertension present before pregnancy or diagnosed before 20 weeks of gestation. It may also be diagnosed if hypertension persists > 6 weeks postpartum.

Definitions and Diagnostic Criteria

Hypertension in Pregnancy: Systolic BP $\ge$ 140 mmHg and/or Diastolic BP $\ge$ 90 mmHg.

To confirm the diagnosis, the BP should be elevated on two occasions, at least 15 minutes apart.

Severe Hypertension

Systolic BP $\ge$ 160 mmHg
Diastolic BP $\ge$ 110 mmHg

⚠️ MCCQE1 Red Flag: Severe Hypertension

Severe hypertension is an obstetrical emergency requiring immediate evaluation and treatment to prevent stroke and congestive heart failure.

Preeclampsia: A Multisystem Disorder

Preeclampsia is no longer defined solely by proteinuria. It is a state of placental hypoperfusion resulting in widespread endothelial dysfunction.

Diagnostic Criteria for Preeclampsia

Must have Hypertension (≥ 20 weeks) PLUS one of the following:

Proteinuria:
- $\ge$ 0.3 g/day in a 24-hour urine collection
- Protein:Creatinine ratio $\ge$ 30 mg/mmol
- $\ge$ 2+ on dipstick (only if quantitative methods unavailable)
Adverse Conditions (End-organ dysfunction):

System	Adverse Conditions
CNS	Headache, visual disturbances, hyperreflexia, clonus, eclampsia (seizures)
Cardiorespiratory	Chest pain, dyspnea, pulmonary edema, SpO2 < 97%
Hematological	Thrombocytopenia (Platelets < 100 x 10^9/L), elevated INR/PTT
Renal	Elevated serum creatinine, oliguria
Hepatic	Elevated transaminases (AST, ALT), RUQ/epigastric pain
Fetoplacental	Fetal growth restriction (FGR), oligohydramnios, abnormal umbilical artery Doppler

HELLP Syndrome

A severe variant of preeclampsia characterized by:

Hemolysis (LDH > 600 IU/L, schistocytes)
Elevated Liver enzymes (AST/ALT > 2x upper limit)
Low Platelets (< 100 x 10^9/L)

Risk Factors

Identifying risk factors allows for the initiation of aspirin prophylaxis.

High Risk Factors

History of preeclampsia
Multifetal gestation
Chronic hypertension
Type 1 or 2 Diabetes
Renal disease
Autoimmune disease (SLE, APS)

Moderate Risk Factors

Nulliparity
Age ≥ 40 years
BMI ≥ 35 kg/m²
Family history of preeclampsia (mother/sister)
Interpregnancy interval > 10 years

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Prophylaxis: SOGC recommends Aspirin (ASA) 81-162 mg daily at bedtime starting between 12-16 weeks gestation for women with 1 high-risk factor or ≥ 2 moderate risk factors.

Investigations Checklist

When evaluating a patient with suspected HDP, consider the following:

Maternal Vitals: BP (appropriately sized cuff), HR, SpO2, Reflexes/Clonus.
CBC: Check for platelets (thrombocytopenia) and Hb (hemoconcentration or hemolysis).
Liver Function: AST, ALT, LDH, Bilirubin.
Renal Function: Creatinine, Uric Acid (hyperuricemia correlates with disease severity).
Coagulation: INR, PTT, Fibrinogen (if suspecting DIC/severe HELLP).
Urinalysis: Protein:Creatinine ratio or 24h urine.
Fetal Assessment: Non-stress test (NST), Biophysical Profile (BPP), Ultrasound for growth and fluid, Umbilical Artery Doppler.

Management: Canadian Guidelines

Management depends on the severity of hypertension, gestational age, and maternal/fetal status.

1. Blood Pressure Targets

Comorbid conditions (Diabetes, Renal disease): Target BP < 140/90 mmHg.
No comorbidities: Target BP < 160/110 mmHg (SOGC suggests treating if sBP $\ge$ 140 or dBP $\ge$ 90 to prevent progression to severe hypertension).

2. Antihypertensive Pharmacotherapy

Commonly used agents in Canada:

Medication	Class	Comments
Labetalol	Alpha/Beta-blocker	First-line. Avoid in asthma or frank heart failure.
Nifedipine	Calcium Channel Blocker	First-line (Extended release). Immediate release (capsule) is contraindicated due to hypotension risk.
Methyldopa	Alpha-2 Agonist	Second-line. Slower onset. Often used for chronic hypertension. Side effect: sedation, depression.
Hydralazine	Direct Vasodilator	Often used IV for acute severe hypertension.

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Contraindicated: ACE Inhibitors (e.g., Ramipril), ARBs (e.g., Valsartan), and Direct Renin Inhibitors are teratogenic (renal failure, oligohydramnios, skull hypoplasia).

3. Acute Management of Severe Hypertension

Severe hypertension ( $\ge$ 160/110) is an emergency.

Step 1: Immediate Assessment

Assess ABCs. Establish IV access. Continuous fetal monitoring.

Step 2: Pharmacotherapy

Administer rapid-acting antihypertensives.

Labetalol: 20 mg IV, repeat 20-80 mg q10-30 min (Max 300 mg).
Nifedipine (PA or XL): 10-20 mg PO q45 min (Max 50 mg).
Hydralazine: 5 mg IV, repeat 5-10 mg q20-30 min (Max 20 mg).

Step 3: Seizure Prophylaxis

Initiate Magnesium Sulfate (MgSO4) if preeclampsia with severe features or eclampsia is present.

4. Seizure Prophylaxis (Magnesium Sulfate)

Indication: Prevention of eclamptic seizures in severe preeclampsia; treatment of active eclamptic seizures.
Mechanism: Cerebral vasodilation and membrane stabilization.
Dosing: 4g IV loading dose over 20 min, followed by 1g/hour maintenance infusion.
Monitoring: Reflexes (loss is first sign of toxicity), Respiratory Rate (depression), Urine Output (oliguria increases risk of toxicity).


# Antidote for MgSO4 Toxicity
Calcium Gluconate 1g IV (10 mL of 10% solution) over 3 minutes.

5. Timing of Delivery

Delivery is the only definitive cure for preeclampsia.

≥ 37 weeks: Delivery is recommended.
34 - 36+6 weeks: Stabilization and delivery are generally recommended, especially with severe features.
< 34 weeks: Expectant management if stable to allow for corticosteroid administration (Betamethasone) for fetal lung maturity. Deliver if maternal or fetal condition deteriorates (e.g., HELLP, eclampsia, abruption, non-reassuring fetal status).

Key Points to Remember for MCCQE1

Differentiation: Distinguish between Gestational HTN (no protein) and Preeclampsia (protein OR adverse conditions).
Visual Disturbances: Scotomata or blurred vision in a pregnant patient is preeclampsia until proven otherwise.
Epigastric Pain: Often due to stretching of the liver capsule (Glisson’s capsule); a sign of severe disease.
Postpartum: Preeclampsia can present up to 6 weeks postpartum. Instruct patients to monitor for headaches/visual changes after discharge.
NSAIDs: Use with caution postpartum in severe hypertension as they can elevate BP and affect renal function.

Sample Question

Clinical Scenario

A 32-year-old G1P0 woman presents to the emergency department at 35 weeks gestation with a complaint of a severe, throbbing headache and “seeing spots.” She has no significant past medical history.

Vitals:

BP: 165/115 mmHg (confirmed on repeat 15 mins later)
HR: 88 bpm
RR: 18/min
Temp: 37.0°C

Physical Exam:

Deep tendon reflexes are 4+ with 2 beats of clonus bilaterally.
Abdomen is soft, non-tender.
Fetal heart rate is 140 bpm.

Urinalysis: 3+ Protein.

Which one of the following is the most appropriate initial pharmacologic intervention to prevent seizures in this patient?

Explanation

The correct answer is:

C. IV Magnesium Sulfate

Explanation: This patient has severe preeclampsia (BP $\ge$ 160/110, headache, visual disturbances, hyperreflexia/clonus). She is at high risk for eclampsia (seizures).

Magnesium Sulfate is the first-line agent for both the prevention and treatment of eclamptic seizures. It is superior to phenytoin and diazepam for this indication.
IV Labetalol and PO Nifedipine are appropriate for blood pressure control (which is also necessary here), but the question specifically asks for the intervention to prevent seizures.
Diazepam and Phenytoin are not first-line for eclampsia prophylaxis or treatment in obstetrics unless MgSO4 is contraindicated or ineffective.

MCCQE1 Strategy: Always identify the specific clinical task in the lead-in question (e.g., “prevent seizures” vs. “lower blood pressure”).

References

Magee LA, et al. SOGC Clinical Practice Guideline No. 307: Diagnosis, Evaluation, and Management of the Hypertensive Disorders of Pregnancy. J Obstet Gynaecol Can. 2014;36(5):416-438. Link to SOGC Guidelines
Butt K, et al. SOGC Clinical Practice Guideline No. 426: Hypertensive Disorders of Pregnancy: Diagnosis, Prediction, Prevention, and Management. J Obstet Gynaecol Can. 2022.
Medical Council of Canada. MCCQE Part I Clinical Decision-Making and Objectives. mcc.ca
UpToDate. Preeclampsia: Clinical features and diagnosis. Accessed 2023.