What is the definition, diagnosis, and management of hypertension in pregnancy, considering factors such as medical history, gestational age, and severity of hypertension?

Hypertension in Pregnancy: Comprehensive Study Guide

Definition and Blood Pressure Thresholds

Hypertension in pregnancy is defined as systolic BP ≥140 mmHg and/or diastolic BP ≥90 mmHg, measured on at least two separate occasions. 1, 2, 3

• Severe hypertension is defined as systolic BP ≥160 mmHg and/or diastolic BP ≥110 mmHg 1, 2, 3
• For severe hypertension, confirmation requires repeated measurements within 15 minutes 2, 3
• For less severe hypertension, confirmation requires repeated readings over several hours on the same visit or on two consecutive antenatal visits 2, 3
• Use Korotkoff phase V (disappearance of sound) for diastolic BP measurement, not phase IV 1

Ambulatory Blood Pressure Monitoring

• Normal 24-hour ambulatory BP before 22 weeks should be below 126/76 mmHg 2
• Normal awake average should be below 132/79 mmHg 2
• Normal sleep average should be below 114/66 mmHg 2
• Ambulatory BP monitoring is superior to conventional measurements in predicting proteinuria, preterm delivery risk, and infant birth weight 1

Classification System

The ISSHP classification divides hypertensive disorders into two temporal categories: hypertension present before or in the first 20 weeks, and hypertension arising de novo at or after 20 weeks' gestation. 1, 2

Hypertension Known Before Pregnancy or Present in First 20 Weeks

• Chronic hypertension: BP ≥140/90 mmHg that either predates pregnancy or develops before 20 weeks of gestation, usually persisting >42 days postpartum 1

  • Complicates 1-5% of pregnancies 1
  • Can be essential (most common, associated with family history and obesity) or secondary (renal parenchymal disorders, fibromuscular hyperplasia, primary hyperaldosteronism) 2, 4
  • May appear normotensive in early pregnancy due to physiological BP fall in first trimester, masking pre-existing hypertension 1

• White-coat hypertension: Elevated clinic BP (≥140/90 mmHg) but normal home or ambulatory BP (<135/85 mmHg) 1, 2, 3

  • Carries increased risk of preeclampsia and requires monitoring 3

• Masked hypertension: Normal clinic BP but elevated BP at other times 1, 2

Hypertension Arising De Novo at or After 20 Weeks

• Transient gestational hypertension: Hypertension detected in clinic that settles with repeated BP readings over several hours 1, 2

  • Carries 40% risk of developing true gestational hypertension or preeclampsia later in pregnancy 1, 2
  • Requires extra monitoring throughout pregnancy, ideally including home BP measurements 2

• Gestational hypertension: New-onset hypertension at or after 20 weeks without proteinuria or other features of preeclampsia 1

  • Complicates 6-7% of pregnancies 1
  • Approximately 20-25% progress to preeclampsia 3, 4
  • Characterized by poor organ perfusion 1
  • Usually resolves within 42 days postpartum 1

• Preeclampsia: Gestational hypertension accompanied by ≥1 new-onset condition at or after 20 weeks 2

  • New-onset proteinuria (≥0.3 g/24h or ≥30 mg/mmol urinary creatinine in spot sample) 1
  • OR renal insufficiency (creatinine elevation) 2
  • OR liver involvement (elevated liver enzymes) 2
  • OR neurological complications (headache, visual disturbance, occipital lobe blindness, hyperreflexia, clonus, convulsions from cerebral edema) 1, 2
  • OR hematological complications (thrombocytopenia, hemolysis) 2
  • OR uteroplacental dysfunction (fetal growth restriction) 2
  • Complicates 5-7% of pregnancies overall, but increases to 25% in women with pre-existing hypertension 1
  • Edema is no longer part of diagnostic criteria (occurs in 60% of normal pregnancies) 1

• Pre-existing hypertension plus superimposed gestational hypertension with proteinuria: Pre-existing hypertension with further worsening of BP and protein excretion ≥3 g/day after 20 weeks 1

• Antenatally unclassifiable hypertension: BP first recorded after 20 weeks when hypertension is diagnosed; requires re-assessment at or after 42 days postpartum 1

  • Women presenting with hypertension at or after 20 weeks with unknown earlier BP should be managed as if they have gestational hypertension or preeclampsia 2

Pathophysiology of Preeclampsia

Preeclampsia pathogenesis involves two fundamental stages: alterations in placental perfusion (stage 1) and maternal systemic syndrome (stage 2). 4

• The placenta is the key trigger; preeclampsia can occur even without uterine distension or a fetus present 4
• In normal pregnancy, spiral arteries undergo extensive remodeling, transforming into dilated vessels that lose smooth muscle and internal elastic lamina layers, extending to the inner third of myometrium 4
• In preeclampsia, vascular remodeling is defective, with only superficial remodeling that never extends beyond the decidual lining 4
• Primarily a disease of first pregnancies and extreme maternal ages 4
• Multiparous women pregnant by a new partner have intermediate risk, suggesting immunological basis 4
• Risk is reduced with longer period of sexual relations before conception; barrier contraceptives increase risk 4

Severe Features and Complications

HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelet count) represents the severe spectrum of preeclampsia. 1, 4, 5

Signs and Symptoms of Severe Preeclampsia

• Right upper quadrant/epigastric pain (liver edema and hepatic hemorrhage) 1
• Headache and visual disturbance (cerebral edema) 1
• Occipital lobe blindness 1
• Hyperreflexia and clonus 1
• Convulsions (eclampsia from cerebral edema) 1

Maternal and Fetal Risks

• Maternal complications: Abruptio placentae, cerebrovascular accident, organ failure, disseminated intravascular coagulation 1
• Fetal complications: Intrauterine growth retardation, prematurity, intrauterine death 1
• Preeclampsia accounts for 25% of all infants with very low birth weight (<1500 g) 1
• Hypertension complicates up to 15% of pregnancies and accounts for about a quarter of all antenatal admissions 1

Diagnostic Workup

Baseline Testing for Chronic Hypertension

All women with chronic hypertension require baseline testing at first diagnosis to facilitate later detection of superimposed preeclampsia. 2

• Complete blood count 2
• Liver enzymes (AST, ALT) 2
• Serum creatinine and electrolytes 2
• Uric acid 2
• Urinalysis with microscopy 2
• Protein-to-creatinine ratio or albumin-to-creatinine ratio 2

Evaluation for Preeclampsia in Gestational Hypertension

• Complete blood count (to assess for hemolysis and thrombocytopenia) 3
• Liver enzymes (to detect hepatic involvement) 3
• Serum creatinine (to assess renal function) 3
• Proteinuria assessment (24-hour urine collection or spot protein-to-creatinine ratio) 1, 3

Management Principles

Severe Hypertension (≥160/110 mmHg)

Systolic BP ≥170 mmHg or diastolic BP ≥110 mmHg is an emergency requiring hospitalization. 1, 6

Acute Treatment Options

• Intravenous labetalol (preferred) 1
• Oral methyldopa 1
• Oral nifedipine 1
• Intravenous sodium nitroprusside remains treatment of choice in hypertensive crises, though prolonged use carries risk of fetal cyanide poisoning 1
• Intravenous hydralazine should no longer be considered due to association with more perinatal adverse effects 1
• Nitroglycerin is drug of choice for preeclampsia with pulmonary edema 1

Non-Severe Hypertension

Current European guidelines recommend initiating drug treatment in pregnant women with persistent BP ≥150/95 mmHg, and at values >140/90 mmHg in women with gestational hypertension (with or without proteinuria), pre-existing hypertension with superimposed gestational hypertension, and hypertension with subclinical organ damage or symptoms. 6

• The current recommendation based on available data is that antihypertensive therapy should be initiated only in women with severe hypertension (≥160/105 mmHg) 7
• However, the CHIPS and CHAP studies are likely to reduce the threshold for initiating treatment 6

Preferred Antihypertensive Agents

• Methyldopa (drug of choice for non-severe hypertension) 1, 6
• Labetalol 1, 6
• Calcium antagonists (most data available for nifedipine) 1, 6
• Atenolol should be given with caution due to association with fetal growth retardation related to duration of treatment 1

Prevention Strategies

Low-dose aspirin is recommended for women with moderate and high risk of preeclampsia. 1, 8

• Supplemental calcium is recommended if low calcium intake 1

Management of Preeclampsia

The ISSHP explicitly recommends against using the term "severe preeclampsia" in clinical practice; instead describe preeclampsia as "with or without severe features." 1, 2

• Delivery at term is recommended for preeclampsia 1
• Magnesium sulfate for eclampsia and preeclampsia with severe features 1
• Antenatal corticosteroids to enhance fetal lung maturity at <34 weeks' gestation if delivery is likely within next 7 days 1
• Oxytocin in third stage of labor 1
• Management of preeclampsia at earlier stages of gestation requires balancing risks of immediate delivery of immature fetus against risks to both mother and child of complications 9

Monitoring During Pregnancy

• Women with transient gestational hypertension should receive extra monitoring throughout pregnancy, ideally including home BP measurements 2
• Women with gestational hypertension should be monitored more frequently than usual during remainder of pregnancy 3
• Approximately 25% of automated home devices differ from standard sphygmomanometry, requiring validation against calibrated devices before clinical use 2

Postpartum Management

• Gestational hypertension usually resolves within 42 days postpartum 1
• Proteinuria should be evaluated at 3 months postpartum 3
• Re-assessment is necessary at or after 42 days postpartum for antenatally unclassifiable hypertension 1

Long-Term Cardiovascular Implications

Women with any hypertensive disorder of pregnancy face significant long-term cardiovascular risks, and annual medical review is advised lifelong. 2, 6

• Women with chronic hypertension have higher risk of developing cardiovascular disease later in life 8
• Women with history of preeclampsia are at high risk of developing cardiovascular disease later in life 6
• Obstetric history should become part of cardiovascular risk assessment in women 6
• Goals include achieving prepregnancy weight by 12 months postpartum and maintaining healthy lifestyle through exercise and optimal body weight 2

Key Clinical Pitfalls to Avoid

• Do not rely on edema for preeclampsia diagnosis (occurs in 60% of normal pregnancies) 1
• Do not use intravenous hydralazine for acute severe hypertension (associated with more perinatal adverse effects) 1
• Do not miss masked chronic hypertension in early pregnancy due to physiological BP fall in first trimester 1
• Do not use Korotkoff phase IV for diastolic BP measurement (use phase V instead) 1
• Do not dismiss transient gestational hypertension as benign (40% risk of progression) 1, 2
• Do not forget baseline testing in chronic hypertension to enable detection of superimposed preeclampsia 2
• Do not use the term "severe preeclampsia" in clinical practice (describe as "with or without severe features") 1, 2