Physiologic Adaptations & Hypertension in Pregnancy

Physiologic adaptations in normal pregnancy

• Blood volume increases by approximately 40% during pregnancy.
• Platelet count can drop below 200 x 10^9/L due to increased blood volume.
• Coagulation factors like fibrinogen and factor VII increase.
• Marked generalized vasodilation occurs, decreasing peripheral resistance.
• Arterial resistance reduces in response to angiotensin II.
• Cardiac output and stroke volume increase.
• Mean arterial pressure decreases by 10 mm Hg.
• Increased renal blood flow and glomerular filtration rate (by 50%) due to vasodilation.
• Creatinine clearance increases, while serum creatinine and urea decrease.
• Increased uric acid clearance and calcium excretion.
• Glucosuria and aminoaciduria are present.
• Endocrine changes occur, including changes in parathyroid, adrenal, weight, and gastrointestinal function.

Hypertension in Pregnancy

• Sustained elevated blood pressure at rest, measured on two occasions at least 6 hours apart.
• Prevalence: 10% of all pregnancies.

Classification

• Pre-eclampsia
• Chronic hypertension (HTN)
• Transient HTN (Gestational HTN)

Pre-eclampsia

• Defined as sustained hypertension with proteinuria and edema (edema not essential for diagnosis).
• Onset occurs after 20 weeks of gestation.
• Accounts for 50% of all hypertension in pregnancies.
• Usually resolves postpartum.

Mild pre-eclampsia

• Most common type, often asymptomatic.
• Characterized by:
  • Blood pressure ≥ 140/90 mm Hg or an increase in systolic BP by 30 mm Hg or diastolic BP by 15 mm Hg above non-pregnant baseline.
  • Proteinuria (1-2+ on dipstick or > 300 mg/24 hr).
  • Edema (non-dependent, hands and face, often associated with excessive weight gain).

Severe pre-eclampsia

• Less common.
• Can be diagnosed based on:
  • Severe hypertension (BP ≥ 160/110 mm Hg).
  • Severe proteinuria (3-4+ on dipstick or > 5 g/24 hr) alone without symptoms.
  • Mild hypertension and proteinuria if signs and symptoms are present:
    • Pulmonary edema
    • Cyanosis
    • Congestive cardiac failure (CCF)
    • Increased serum creatinine, oliguria
    • Elevated liver function tests (LFTs), right upper quadrant (RUQ) or epigastric pain
    • Visual disturbances (e.g., scotomas, loss of peripheral vision), headache, convulsions
    • Severe nausea and vomiting
    • Thrombocytopenia, microangiopathic hemolysis

HELLP Syndrome

• A type of severe pre-eclampsia.
• Hemolysis, Elevated Liver enzymes, Low Platelets.

Eclampsia

• Latin for convulsions.
• Unexplained tonic-clonic seizures with mild or severe pre-eclampsia.
• Most commonly occurs intrapartum (50%), but can also occur antepartum and postpartum.

Chronic HTN

• Patient may have any underlying disease causing HTN, such as:
  • Essential HTN
  • Arteriosclerosis and chronic glomerulonephritis
  • Chronic pyelonephritis
  • Systemic lupus erythematosus (SLE)

Uncomplicated Chronic HTN

• Pre-existing HTN
• HTN diagnosed ≤ 20 weeks' gestation.
• HTN persisting ≥ 6 weeks postpartum.
• Not induced by pregnancy.

Complicated Chronic HTN (Superimposed preeclampsia)

• Isolated hypertension without proteinuria.
• Characterized by:
  • Worsening hypertension ± proteinuria
  • Symptoms of severe pre-eclampsia late in pregnancy.

Transient HTN

• Late HTN (Gestational HTN).
• Non-sustained (transient) increase in blood pressure without proteinuria or symptoms in the latter half of pregnancy.
• No impact on pregnancy outcome.

Risk Factors

• Maternal Factors

  • Demographic criteria:
    • Primipara (first pregnancy) is the most common risk factor.
    • Age extremes (≤ 18 years or ≥ 34 years).
  • Medical complications:
    • Diabetes mellitus (DM)
    • Chronic HTN
    • Pre-existing renal disease
    • SLE
  • Past or family history (FHx) of pregnancy-induced hypertension.

• Fetal Factors

  • Hydatidiform mole

  • 1 fetus

  • Fetal hydrops
  • Intrauterine growth restriction (IUGR)