Hypertension in pregnancy

Background

Definition

• SBP ≥140 or DBP ≥90, with severe ≥160/110
• Use the muffling of Karotkoff sounds rather than disappearance

Classification

• Pre-existing or chronic hypertension (<20 weeks; 1%), either primary or secondary
  • Often the first time they're seeing a doctor for blood pressure
  • Consider if there is an underlying secondary cause
  • Can have superimposed preeclampsia in 15-20% of these patients
    • Highest risk in patients who started hypertensive and have been trending upwards over the first and second trimesters
• Gestational (>20 weeks; 5%)
  • Mild
  • Severe: BP ≥160/110
• Preeclampsia (1-2%): also have proteinuria or end-organ damage
• Other
  • Transient
  • Masked
  • White coat

Pathophysiology

• BP in pregnancy naturally decreases to a nadir at 20 weeks

Epidemiology

• Affects 8% of all pregnancies
  • Pre-existing in 1%
  • Gestational in 5-6%
  • Preeclampsia in 1-2%
  • Other
• A major cause of maternal and perinatal morbidity and mortality
  • Preeclampsia/eclampsia is the second leading direct cause of maternal mortality in developed world

Differential Diagnosis

• Spurious or transient (white coat hypertension)
• Pre-existing (especially if in first trimester)
• Gestational (>20 weeks gestation)
  • No proteinuria
    • Mild gestational hypertension
      • Presents late ≥37 weeks
      • Outcomes are fine
    • Severe gestational hypertension
      • Very high risk for preeclampsia within 5 weeks if presents <34 weeks
  • Proteinuria or end-organ dysfunction (preeclampsia)
    • Two-stage model
      • 1. Failure of maternal spiral arteries to re-model
      • 2. Multi-system process characterized by hypertension and end-organ dysfunction due to a dysfunctional endothelium
        • Cardiorespiratory: hypertension, myocardial dysfunction
        • CNS: eclampsia, TIA/stroke, PRES
        • Renal: glomerular endotheliosis, proteinuria, ATN, AKI
        • Hepatic: HELLP, hepatic dysfunction
        • Hematologic: mAHA, thrombocytopenia, DIC
    • Two leading theories
      • Excessive shedding of syncitiotrophoblasts into maternal circulation in women with preeclampsia, which presents late and mildly
      • Increased concentrations of soluble receptor for angiogenic factors (VEGF agonists, including s-Flt and PLGF)

Management

Chronic Hypertension

• First-line antihypertensives: labetalol, methyldopa, nifedipine, hydralazine
• Second-line is hydrochlorothiazide, but it has a theoretical risk of decreasing placental perfusion
• Third-line includes clonidine, prazosin
• Fourth-line: nitrates (short term use)
• Antihypertensives often need to be titrated throughout pregnancy
• Avoid: ACEi and ARBs
  • ACE inhibitors cause fetal anuria and oligohydramnius in T2-3
    • Unclear teratogenicity in T1
  • ARBs may be worse
  • Stop these medications when patient starts trying to conceive
• Target
  • No comorbidities: 130-155/80-105
  • With comorbidities 130-139/80-89

Preeclampsia

• Prevention
  • ASA 75-100mg daily prior to 16 weeks
  • Calcium 1000mg daily
• Severe HTN >160/109
  • Treat if symptomatic, monitor if not
  • Target <155/95 for maternal safety while allowing placental perfusion to continue
• Labetalol, nifedipine, hydralazine IV
  • Labetalol 20mg IV x1 repeated q30min up to 300mg then switch to oral
  • Nifedipine 5-10mg PO q30min
  • Hydralazine 5-10mg IV q30min up to 20mg
• MgSO₄ 4-6g in 100mL D5W over 15 minutes, then 1-2g/h for 24h
  • Beware toxicity, especially if oliguric
    • CNS depression, decreased reflexes
    • Respiratory depression, bradycardia, hypotension
• Deliver if cannot control blood pressure, they develop symptoms, of they have evidence of end-organ involvement
  • HELLP, acute kidney injury, DIC, pulmonary edema, neurologic events
  • If you can stabilize BP, though, can get better fetal outcomes
• Postpartum: AVOID NSAIDs

Postpartum

• If breastfeeding, can use same meds as above, with addition of captopril or enalapril and hydrochlorothiazide

Further Reading

• Magee LA et al. Diagnosis, evaluation, and management of the hypertensive disorders of pregnancy. Pregnancy Hypertens. 2014;4(2):105-145.
• CHIPS. Less-Tight versus Tight Control of Hypertension in Pregnancy. N Engl J Med. 2015; 372:407-417.