3.1 Classification & Diagnosis of Hypertensive Disorders of Pregnancy

Hypertensive disorders complicate approximately 8% to 10% of all pregnancies worldwide and remain a leading cause of maternal and perinatal morbidity and mortality. For the Certified Nurse-Midwife (CNM), precise differentiation between chronic hypertension, gestational hypertension, preeclampsia, eclampsia, and HELLP syndrome is fundamental to antepartum risk stratification, collaborative practice, and timely intervention.

Diagnostic Classification of Hypertensive Disorders in Pregnancy

The American College of Obstetricians and Gynecologists (ACOG) and the American College of Nurse-Midwives (ACNM) classify hypertensive disorders into five major clinical categories based on gestational age at onset, the presence of proteinuria, and end-organ systemic involvement.

Deep-Dive Clinical Criteria & Pathophysiology

Chronic Hypertension and Superimposed Preeclampsia

Chronic hypertension is defined as high blood pressure documented prior to pregnancy or before 20 weeks gestation, or hypertension that was initially diagnosed during pregnancy but persists beyond 12 weeks postpartum.

• Contemporary Management (CHAP Trial Update): In accordance with the Chronic Hypertension and Pregnancy (CHAP) trial findings, treatment of mild chronic hypertension to a blood pressure target of <140/90 mmHg (rather than the historical threshold of 160/105 mmHg) significantly reduces the incidence of superimposed preeclampsia, preterm birth, placental abruption, and cardiovascular complications without impairing fetal growth.
• Preferred First-Line Oral Agents: Oral labetalol (100–400 mg twice to three times daily), extended-release nifedipine (30–90 mg once daily), and methyldopa (250–500 mg two to three times daily).
• Absolute Contraindications: Angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), direct renin inhibitors, and mineralocorticoid receptor antagonists are strictly contraindicated throughout pregnancy due to risks of fetal renal dysgenesis, oligohydramnios sequence, pulmonary hypoplasia, calvarial hypoplasia, and intrauterine fetal demise.
• Superimposed Preeclampsia: Occurs in 20% to 50% of women with chronic hypertension. Diagnosed when there is a sudden, refractory escalation in baseline blood pressure, new onset of proteinuria in a woman previously without it, a dramatic sudden increase in baseline proteinuria, or the emergence of any systemic severe features (thrombocytopenia, hepatic transaminitis, renal insufficiency, or neurologic symptoms).

Preeclampsia Diagnostic Criteria: The Modern Paradigm

Historically, proteinuria was mandatory for the diagnosis of preeclampsia. Current diagnostic guidelines recognize that preeclampsia is a multisystem endothelial disorder; therefore, proteinuria is no longer required if other systemic manifestations are present.

In a woman with new-onset hypertension after 20 weeks gestation (SBP ≥140 mmHg or DBP ≥90 mmHg on two occasions at least 4 hours apart), preeclampsia is established if any of the following criteria are met:

1. Proteinuria:
   • ≥300 mg per 24-hour urine collection (gold standard), OR
   • Urine protein-to-creatinine ratio (uPCR) ≥0.3 mg/mg (or ≥30 mg/mmol), OR
   • Urine dipstick reading of 2+ or greater (used only if quantitative methods are unavailable).
2. Thrombocytopenia: Platelet count <100,000/μL.
3. Renal Insufficiency: Serum creatinine concentration >1.1 mg/dL, or a doubling of the baseline serum creatinine in the absence of other intrinsic renal disease.
4. Impaired Liver Function: Elevated blood concentrations of liver transaminases (alanine aminotransferase [ALT] or aspartate aminotransferase [AST]) to twice the upper limit of normal, or severe persistent right upper quadrant or epigastric pain unresponsive to medication and not accounted for by alternative diagnoses.
5. Pulmonary Edema: Clinical and radiographic evidence of alveolar fluid accumulation.
6. New-Onset Headache and Visual Symptoms: Persistent, severe, throbbing headache unresponsive to standard analgesics (e.g., acetaminophen) and visual scotomata, photopsia, diplopia, or cortical blindness.

Midwifery Pearl: Massive proteinuria (historically defined as >5 grams/24 hours) and fetal growth restriction (FGR) have been deliberately removed from the diagnostic criteria for severe features in contemporary guidelines. While massive proteinuria warrants clinical vigilance, it does not by itself dictate immediate delivery in the absence of other severe features.

HELLP Syndrome

HELLP syndrome represents a severe, life-threatening variant of preeclampsia characterized by microangiopathic hemolytic anemia, hepatic necrosis, and profound consumptive thrombocytopenia. Up to 15% to 20% of patients with HELLP syndrome do not exhibit antecedent hypertension or overt proteinuria, presenting a major diagnostic pitfall.

• Hemolysis (H): Microangiopathic hemolysis demonstrated by abnormal peripheral blood smear with schistocytes, helmet cells, or burr cells; elevated total bilirubin (≥1.2 mg/dL, primarily indirect); low or undetectable serum haptoglobin (<25 mg/dL); and markedly elevated serum lactate dehydrogenase (LDH >600 IU/L).
• Elevated Liver Enzymes (EL): Serum AST or ALT elevated to at least twice the upper limit of institutional normal (typically AST ≥70 IU/L), reflecting periportal sinusoidal fibrin deposition and hepatocellular necrosis.
• Low Platelets (LP): Platelet count <100,000/μL (Mississippi Class 1: <50,000/μL; Class 2: 50,000–100,000/μL; Class 3: 100,000–150,000/μL).
• Complications: Subcapsular liver hematoma, hepatic rupture, disseminated intravascular coagulation (DIC; present in 20%), placental abruption, acute renal failure, and pulmonary edema.