Hypertension in Pregnancy

Epidemiology

  • Hypertension affects 10-15% of all pregnancies
    • Up to 25% of all antenatal consultations are regarding hypertension
  • Mild pre-eclampsia affects 10% of primigravid women
  • Severe pre-eclampsia affects 1% of primigravid women
  • Eclampsia affects 1 in 2000 pregnancies
    • Death from eclampsia is 2%
  • Pre-eclampsia is the most common cause of iatrogenic prematurity

Physiology

  • BP Ξ Systemic vascular resistance and cardiac output
  • In pregnancy, there is systemic vasodilation caused by high levels of circulating relaxin and β-hCG
    • This causes an initial drop in BP during the first trimester (peak drop of around 10mmHg at 22-24 weeks
    • However, from then onwards there is a progressive rise in BP to term (note there may be a drop in BP in the third trimester if the baby is pressing on the IVC).  This is likely to be due to the other CVS changes e.g. increased circulating volume (will rise by up to 50% at term), increased cardiac output etc.

Definition

  • Hypertension during pregnancy is defined as a BP >= 140/90mmHg on >1 occasion or a DBP >=110mmHg on one occasion.
    • Mild is 140-149mmHg SBP or 90-99mmHg DBP
    • Moderate is 150-159mmHg SBP or 100-109mmHg DBP
    • Severe is >110mmHg DBP or >160mmHg SBP

Types

Pre-existing (essential) chronic hypertension

  • >140/90mmHg before pregnancy OR before 20 weeks gestation (OR patients already on BP lowering drugs)
  • This is the most common cause of hypertension during pregnancy
    • it is usually known about BUT may be discovered after pregnancy when the mother’s BP fails to return to normal (retrospective dx)
  • Causes
    • Most will be benign essential hypertension BUT other causes should be considered e.g.
      • Renal (Polycystic kidney; glomerulonephritis; renovascular disease); endocrine (Cushing’s; phaeochromocytoma; thyroid disease; Conn’s syndrome); Cardiac (atherosclerosis; MI etc)
  • Risks
    • There is a higher risk of pre-eclampsia (careful monitoring of BP should be done to note any further, worrying increase)
    • There is a risk of intra-uterine growth restriction (IUGR)
    • There is also a risk of placental abruption
  • Assessment
    • It is important to ask about symptoms of pre-eclampsia (see below) and assess for proteinuria at every antenatal visit
      • Also ask about prior pregnancies and their management
  • Management
    • Prescribe aspirin 75mg daily from 12 weeks gestation
    • STOP any ACE inhibitors or Angiotensin receptor blockers and switch to an alternative (other medications for BP should be continued)
    • Aim for BP<150/100mmHg (but DBP >80mmHg)
      • If there is target organ damage- <140/90mmHg
    • Monitor BP and risk of pre-eclampsia closely (advice on onset of symptoms and need to see a doctor)

Pregnancy induced Hypertension (PIH)

  • NB This can only occur in the latter half of pregnancy and will resolve within 6 weeks of delivery
  • The feature of PIH is ONLY hypertension i.e. NO other symptoms of pre-eclampsia
    • BUT there is an increased chance of developing pre-eclampsia
  • Management
    • Monitor closely for proteinuria/onset of symptoms of pre-eclampsia
      • If urine is negative
        • consider admission if hypertension is severe (see management below)
        • in moderate hypertension, prescribe oral labetalol first line to keep DBP between 80 and 100mmHg and SBP <150mmHg
          • Measure BP at least once a week
      • If urine is positive, consider urgent referral/admission for assessment

Pre-eclampsia

  •  New hypertension (>20 weeks gestation) with significant proteinuria
    • NB Pre-eclampsia can be new but superimposed on chronic hypertension
    • Significant proteinuria is >300mg in 24 hours or >30mg/mmol in a spot urinary PCR
  • Risk factors for pre-eclampsia
    • Major (1 required)
      • A history of hypertensive disease in pregnancy
      • CKD
      • Autoimmune disease
      • Diabetes mellitus
      • Chronic hypertension
      • Thrombophilia
    • Minor (2 or more are high risk)
      • First pregnancy
      • Age >40
      • Pregnancy interval >10 years
      • Obesity
      • Family history of preeclampsia
      • Multiple pregnancy
    • Management of high risk patients
      • Prescribe 75mg aspirin daily from 12 weeks gestation until birth
  • Symptoms
    • Severe headaches (increasing frequency and unrelieved by regular analgesia)
    • Visual disturbance e.g. blurred vision, flashers/floaters, double vision
    • Persistent new epigastric pain or RUQ pain
    • Vomiting
    • Breathlessness
    • Sudden swelling of the face, hands, feet

Management of Pre-eclampsia and severe hypertension warranting admission

  • Labetalol (first line) to try and keep DBP between 80 and 100mmHg and SBP <150mmHg
    • Methyldopa or nifedipine second line
  • Blood tests to assess renal and liver function, electrolytes, FBC
  • Timing of birth
    • For pre-eclampsia/severe hypertension <34 weeks, delivery can be discussed if severe refractory hypertension develops or if there are other maternal or foetal indications for delivery
      • Do not offer birth to patients with mild-moderate PIH (BP <160/110mmHg) until 37 weeks
    • Delivery should be offered >34 weeks for patients with controllable severe pre-eclampsia
      • Depends on maternal/foetal condition, risk factors, availability of neonatal care
    • >37 weeks, patients with mild-moderate pre-eclampsia should be induced 

Proteinuria without hypertension

  • Consider UTI or, if there are no clinical feaures, possibility of renal disease/CKD in patients <20 weeks
  • In patients >20 weeks, with 2+ or more proteinuria, refer to specialist (even if symptomatic of a UTI)

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