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diagnosis and screening for pre-eclampsia

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The BHS criteria for the diagnosis of pre-eclampsia is (1):

  • either a rise in blood pressure of >=15 mmHg diastolic or >= 30 mmHg systolic from early pregnancy
  • or diastolic blood pressure of >= 90 mmHg on 2 occasions 4 hours apart or >= 110 mmHg on 1 occasion and proteinuria (1+ is an indication for referral and >=300mg/24 hours is a criterion for diagnosis)

These definitions include only raised blood pressure and proteinuria but 30% of eclamptic convulsions occur in the absence of either of these criteria. Also, a systolic pressure of 160 mmHg in pregnancy requires referral to a specialist.

However a more recent BMJ review has suggested the following classification of hypertensive disorders in pregnancy (2):

  • gestational hypertension (pregnancy induced hypertension)
    • hypertension detected for the first time after 20 weeks' gestation, in the absence of proteinuria
    • hypertension defined as systolic blood pressure 140 mm Hg or diastolic blood pressure 90 mm Hg
    • resolves within three months after the birth
  • pre-eclampsia and eclampsia
    • hypertension and proteinuria detected for the first time after 20 weeks' gestation
    • hypertension defined as above Proteinuria defined as 300 mg/day or 30 mg/mmol in a single specimen or 1+ on dipstick
    • eclampsia is the occurrence of seizures superimposed on the syndrome of pre-eclampsia
    • the review notes that ".. A relative rise in blood pressure or oedema is not related to out-come, and neither is an indication for routine screening..."
  • chronic hypertension - known hypertension before pregnancy; or a rise in blood pressure to more than 140 / 90 mmHg before 20 weeks
    • "Essential" hypertension if there is no underlying cause
    • "Secondary" hypertension if associated with underlying disease
  • 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

The BMJ review notes that (2):

  • assessment usually begins when a woman presents to a general practitioner or midwife requesting antenatal care
    • if a women at high risk are then offered further visits and testing, with referral for specialist care
      • factors associated with high risk of pre-eclampsia include:
        • primagravida
        • previous pre-eclampsia
        • a period of 10 years or more since previous pregnancy
        • woman >= 40 years of age
        • a body mass index >= 35 at booking in
        • if there is a family history of pre-eclampsia (especially mother or sister)
        • if the booking diastolic blood pressure >= 80 mm Hg
        • multiple pregnancy
        • if there is an underlying medical condition:
          • diabetes
          • chronic hypertension
          • renal disease
          • presence of antiphospholipid antibodies
    • screening of low risk women is based primarily on blood pressure measurement and urine analysis
    • if a woman has a blood pressure > 140/90 mm Hg then she should be referred for specialist assessment
    • proteinuria should ideally be confirmed in a 24 hour collection
    • diagnosis of pre-eclampsia is more certain if other organ systems are implicated e.g. persistent severe headache; persistent new epigastric pain; visual disturbances (such as blurred vision, diplopia, or floating spots); vomiting; hyperreflexia, with brisk tendon reflexes; severe swelling of hands, face, or feet of sudden onset; serum creatinine concentration increased (> 110 µmol/l); reduced platelet count to < 100x10^9/l; evidence of microangiopathic haemolytic anaemia; liver enzyme activity elevated (alanine aminotransferase, aspartate aminotransferase, or both)
    • automated blood pressure monitors systematically underestimate blood pressure in pregnancy and pre-eclampsia. If used, they should be calibrated regularly against a mercury sphygmomanometer
  • NICE suggest a methodology for blood pressure measurement in pregnancy (3)
    • remove tight clothing, ensure arm is relaxed and supported at heart level
    • use cuff of appropriate size
    • inflate cuff to 20-30 mmHg above palpated systolic blood pressure
    • lower column slowly, by 2 mmHg per second or per beat
    • read blood pressure to the nearest 2 mmHg
    • measure diastolic blood pressure as disappearance of sounds (phase V).

Reference:

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