Hypertension in Pregnancy

Introduction

Hypertension is defined as a sustained blood pressure higher than 140/90 mmHg and may be attributable to any of the conditions summarized in Box 35.1. It affects 20–30% of American adults and complicates as many as 5–8% of all pregnancies. Approximately 15% of maternal deaths are attributable to hypertension, making it the second leading cause of maternal mortality in the United States. The classification system of hypertension in pregnancy proposed by the National High Blood Pressure Education Program Working Group is summarized in Box 35.2.

Chronic hypertension

Chronic hypertension complicates as many as 5% of pregnancies and is characterized by a history of high blood pressure before pregnancy, elevated blood pressure during the first half of pregnancy, or elevated blood pressure that persists beyond 12 weeks post partum. Blood pressure is measured in a sitting position with the arm at the level of the heart and multiple measurements are obtained. Other physical findings may include a renal artery bruit, funduscopic abnormalities, an enlarged thyroid gland, diminished peripheral pulses, skin and joint abnormalities.

Laboratory tests include a complete blood count, glucose screen, electrolyte panel, serum creatinine, urinalysis and urine culture. In some cases, additional tests may be needed. In patients with possible renal disease (serum creatinine ≥ 0.8 mg/dL, urine protein > 1 + on dipstick), a 24-h urine collection for creatinine clearance and total protein will provide baseline information that may be helpful in diagnosing the onset of pre-eclampsia later in pregnancy. Additional tests may include antinuclear antibody, thyroid-stimulating hormone, urinary catecholamines, electrocardiogram and chest x-ray.

Box 35.1 Causes of chronic hypertension

Idiopathic

Essential hypertension

Vascular disorders

Renovascular hypertension

Aortic coarctation

Endocrine disorders

Diabetes mellitus

Hyperthyroidism

Pheochromocytoma

Primary hyperaldosteronism

Hyperparathyroidism

Cushing’s syndrome

Renal disorders

Diabetic nephropathy

Chronic renal failure

Acute Renal Failure

Tubular necrosis

Cortical necrosis

Pyelonephritis

Chronic glomerulonephritis

Nephrotic Syndrome

Polycystic kidney

Connective tissue disorders

Systemic lupus erythematosus

Fetal assessment in chronic hypertension

Chronic hypertension, regardless of the cause, increases the risk of poor fetal growth. An initial ultrasound examination should be performed as early as possible to confirm the dates and exclude fetal anomalies. Thereafter, fetal growth usually is assessed every 2–4 weeks. Antepartum fetal monitoring is initiated by 32–34 weeks. Doppler velocimetry of the umbilical, uterine and middle cerebral arteries is helpful in optimizing the timing of delivery, particularly in cases of fetal growth restriction.

Box 35.2 Classification of hypertension in pregnancy

Definition of Hypertension

Mild: Systolic blood pressure ≥140 mmHg

Diastolic blood pressure ≥90 mmHg

Severe: Systolic blood pressure ≥180 mmHg

Diastolic blood pressure ≥110 mmHg

Chronic Hypertension

Hypertension with onset before pregnancy or before 20th week of gestation

Use of antihypertensive medications before pregnancy

Persistence of hypertension beyond 12 weeks postpartum

Pre-eclampsia

Hypertension that occurs after 20 weeks of gestation in a woman with previously normal blood pressure. SBP ≥ 140 mmHg or DBP ≥ 90 mmHg on two occasions at least 6 hours apart

Proteinuria, defined as urinary excretion of 0.3 g protein or higher in a 24-hour urine specimen. This finding usually correlates with a finding of 1 + or greater on dipstick

Note edema is no longer a diagnostic criterion

Note a systolic rise of 30 mm Hg or a diastolic rise of 15 mm Hg no longer diagnostic criteria

Eclampsia

New-onset grand mal seizures in a woman with pre-eclampsia that cannot be attributed to other causes

Superimposed Pre-eclampsia – Eclampsia

Pre-eclampsia or eclampsia that occur in a woman with preexisting chronic hypertension

Gestational Hypertension

Hypertension detected for the first time after midpregnancy

Distinguished from pre-eclampsia by the absence of proteinuria

Working diagnosis only during pregnancy

Transient hypertension of pregnancy

Gestational hypertension that resolves by 12 weeks postpartum