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Hypertension in pregnancy - Background information
What is it?

  • Several different hypertensive disorders can complicate pregnancy, and numerous different terms and definitions are used to describe them.
  • Working definitions used by the National Institute for Health and Clinical Excellence (NICE) are [National Collaborating Centre for Women's and Children's Health, 2010]:
    • Hypertension during pregnancy
      • A diastolic blood pressure of 90 mmHg or greater on two occasions more than 4 hours apart, and/or
      • A single diastolic blood pressure reading greater than 110 mmHg.
    • Mild, moderate, and severe hypertension
      • Mild hypertension: diastolic blood pressure of 90–99 mmHg and/or systolic blood pressure of 140–149 mmHg.
      • Moderate hypertension: diastolic blood pressure of 100–109 mmHg and/or systolic blood pressure of 150–159 mmHg.
      • Severe hypertension: diastolic blood pressure of 110 mmHg or greater and/or systolic blood pressure of 160 mmHg or greater.
    • Chronic hypertension
      • Hypertension that is present at the booking visit, or before 20 weeks' gestation, or in a woman already on antihypertensive medication (as the blood pressure tends to fall during the first and second trimesters, a woman with a high blood pressure before week 20 of pregnancy can be assumed to have pre-existing hypertension).
    • Gestational hypertension
      • New hypertension presenting after 20 weeks' gestation without significant proteinuria.
    • Pre-eclampsia
      • New hypertension presenting after 20 weeks' gestation with significant proteinuria. Pre-eclampsia is a multi system disorder which can affect the placenta, kidney, liver, brain, and other organs of the mother. It is thought to be due to widespread endothelial cell damage secondary to an ischaemic placenta, although the exact cause is unknown.
      • Pre-eclampsia superimposed on chronic hypertension: onset of new signs or symptoms of pre-eclampsia after 20 weeks' gestation in a woman with chronic hypertension [Duley et al, 2006].
      • HELLP syndrome (Haemolysis, Elevated Liver enzymes, and Low Platelets syndrome) is a severe form of pre-eclampsia. It is essentially a laboratory diagnosis.
    • Eclampsia is the occurrence of one or more seizures in a woman with pre-eclampsia.
    • Significant proteinuria is more than 300 mg protein in a 24-hour urine collection or more than 30 mg/mmol in a spot urinary protein/creatinine sample.

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