Hypertensive Disorders in Pregnancy – Basics

Hypertensive disorders in pregnancy is a term that encompass wide range of blood pressure related disorders during pregnancy like gestational hypertension, pre-eclampsia, eclampsia, etc.

Blood pressure in Normal Pregnancy:

During middle trimester, due to the reduction in Systemic Vascular Resistance (SVR) and Arterio-venous (AV) shunting within the uterus and intervillous space – the Blood Pressure (BP) falls below pre-pregnancy or early pregnancy level. This is compensated by relative tachycardia. In the 3rd trimester, BP usually rises back to the pre-pregnancy level.

Criteria for diagnosis of hypertensive disorders in pregnancy:

  • If previous Blood pressure (BP) is not known: Absolute BP ≥140/90 mm Hg, taken on two separate occasions 6 hours apart
  • If pre-pregnant or first trimester BP is known: Systolic BP + ≥30 mmHg and Diastolic BP + ≥15 mmHg

Classification of Hypertensive disorders in pregnancy:

1. Chronic hypertension: Hypertension diagnosed before pregnancy or before 20 weeks of pregnancy. It can be either essential or secondary.

2. Pregnancy Induced Hypertension (PIH): New onset hypertension diagnosed after 20 weeks of pregnancy. It includes:

  • Gestational Hypertension
  • Pre-eclampsia
  • Eclampsia

Pre-eclampsia and Eclampsia are often referred to as Toxemia of pregnancy.

ClassificationGestational weeksBlood pressure (mmHg)ProteinuriaSeizuresAdditional features
Gestational hypertension> 20> 140/90NoNo
Mild pre-eclampsia> 20140-160/90-110>300mg/24 hrs or ≥1+ dipstickNo
Severe pre-eclampsia>20>160/110>5g/24 hrs ≥3+ dipstickNoEnd-organ dysfunction
Eclampsia>20>160/110>5g/24 hrsYesEnd-organ dysfunction
Chronic hypertension<20 or prior to pregnancy>140/90NoNo
Superimposed pre-eclampsia<20>140/90New onset >0.5 g/2 hrsNoThrombocytopenia or Raised Liver enzymes

Incidence of hypertensive disorders in pregnancy:

  • About 10% pregnant women develop hypertension and mild pre-eclampsia
  • Further 10% of these develop severe pre-eclampsia
  • Incidence of eclampsia ranges from 1 in 500 to 1 in 30

Risk Factors for hypertensive disorders in pregnancy:

  1. Primigravida
  2. Positive family history and past history
  3. Placental abnormalities:
    • Hyperplacentosis: Molar pregnancy, Multiple pregnancy, Diabetes mellitus
    • Placental ischemia
  4. Obesity
  5. New partner
  6. Chronic hypertension
  7. Thrombophilias: Antiphospholipid syndrome, Protein C or S deficiency, Factor V Leiden

Pathophysiology:

Trophoblast invasion

In normal pregnancy, cytotrophoblasts invade the uterine spiral arterioles, converting them from small-caliber vessels to large-caliber capacitance vessels capable of carrying larger amount of blood flow through the placenta. In pre-eclampsia events are postulated to occur in following steps:

  1. Defective cytotrophoblast invasion
  2. Deficient transformation of the spiral arterioles
  3. Reduced placental perfusion
  4. Increased secretion of antiangiogenic factor from hypoperfused placenta
  5. Antagonism of proangiogenic effects of vascular endothelial growth factor (VEGF) and placental growth factor
  6. Systemic vascular endothelial dysfunction
  7. Increased production of reactive oxygen species (ROS), thromboxane (TX-A2), and endothelin-1 (ET-1) and Increased vascular sensitivity to angiotensin II and decreased nitric oxide (NO) and prostacyclin (PGI2) bioavailability
    Pre-eclampsia pathophysiology
  8. Potent vasoconstriction and end-organ damage:
    • Neurologic: Headache, Blurred vision, Visual scotomata, Hyperreflexia, Clonus, and seizures. Cerebral edema and intracerebral hemorrhage can be seen.
    • Renal: Proteinuria (>300 mg/day), Azotemia (decreased renal blood flow and average GFR by 30-40%), Acute Kidney Injury (usually due to Acute Tubular Necrosis), Increased urate reabsorption (leads to hyperuricemia)
    • Hematologic: Microangiopathic hemolytic anemia, Thrombocytopenia, DIC (Disseminated Intravascular Coagulation)
    • Hepatic: HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets)
    • Cardiovascular: Hypertension, decreased cardiac output
    • Gastrointestinal: Elevated liver enzymes, epigastric/right upper quadrant pain, subcapsular hemorrhage, liver rupture
    • Other: Pulmonary edema, Peripheral edema

 

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