Preeclampsia is a disorder of widespread vascular endothelial malfunction and vasospasm that occurs after 20 weeks' gestation. It is clinically defined by hypertension and proteinuria.
Preeclampsia is part of a spectrum of disorders that includes gestational hypertension, severe preeclampsia, and eclampsia. Although each of these disorders can appear in isolation, they are thought of as progressive manifestations of a single process and are believed to share a common etiology.
The diagnostic criteria for preeclampsia focus on measurement of elevated blood pressure and proteinuria that develop after 20 weeks' gestation. Consensus is lacking among the various national and international organizations about the values that define the disorder, but a reasonable limit in a woman who was normotensive prior to 20 weeks' gestation is a systolic blood pressure (BP) greater than 140 mm Hg and a diastolic BP greater than 90 mm Hg on 2 successive measurements 4-6 hours apart. Preeclampsia in a patient with preexisting essential hypertension is diagnosed if systolic BP has increased by 30 mm Hg or if diastolic BP has increased by 15 mm Hg.
Proteinuria is defined as 300 mg or more of protein in a 24-hour urine sample. In the emergency department, a urine protein-to-creatinine ratio of 0.19 or greater is somewhat predictive of significant proteinuria (negative predictive value [NPV], 87%).1 Serial confirmations 6 hours apart increase the predictive value. Although more convenient, a urine dipstick value of 1+ or more (30 mg/dL) is not reliable.
For the purposes of guiding management, a distinction can be made between mild preeclampsia and severe preeclampsia.
Diagnostic criteria for severe preeclampsia include at least one of the following:
- Systolic BP greater than 160 mm Hg or diastolic BP greater than 110 mm Hg on 2 occasions 6 hours apart with the patient at bed rest
- Proteinuria greater than 5000 mg in a 24-hour collection or more than 3+ on 2 random urine samples collected at least 4 hours apart
- Oliguria with less than 500 mL per 24 hours
- Persistent maternal headache or visual disturbance
- Pulmonary edema or cyanosis
- Concerning abdominal pain
- Impaired liver function test findings
- Thrombocytopenia
- Oligohydramnios, decreased fetal growth, or placental abruption
Eclampsia is defined as seizures in a patient with preeclampsia.
For more information, see Medscape’s Pregnancy Resource Center.
For a related CME activities, see CME - Hypertension in Pregnancy: Emerging Risk Factor for Cardiovascular Disease, CME/CE – Folic Acid in Early Second Trimester May Reduce Risk of Preeclampsia, and CME – Antioxidants May Not Reduce Risk for Preeclampsia.
Pathophysiology
The mechanism by which preeclampsia occurs is not certain, and the diagnosis may represent a diversity of pathophysiologies that proceed to a common final pathway. The inciting event is believed to be placental hypoperfusion, which may result because the uteroplacental spiral arterioles are abnormally formed, leaving them highly sensitive to vasoconstriction. Both maternal and paternal factors have been implicated in the development of preeclampsia.
Placental hypoperfusion leads by an unclear pathway to the release of systemic vasoactive compounds that cause an exaggerated inflammatory response, vasoconstriction, endothelial damage, capillary leak, hypercoagulability, and platelet dysfunction, all of which contribute to organ dysfunction and the various clinical features of the disease.
Preeclampsia is a state of high systemic vascular resistance with normal or relatively low intravascular volume.
Frequency
United States
Preeclampsia occurs in approximately 5% of all pregnancies. The incidence of preeclampsia is 23.6 cases per 1,000 deliveries in the United States.
International
The global incidence of preeclampsia has been estimated at 5-14% of all pregnancies.
Mortality/Morbidity
Preeclampsia is the third leading pregnancy-related cause of death, after hemorrhage and embolism. Preeclampsia is the cause in an estimated 790 maternal deaths per 100,000 live births.
Morbidity and mortality is related to systemic endothelial dysfunction; vasospasm and small-vessel thrombosis leading to tissue and organ ischemia; CNS events such as seizures, strokes, and hemorrhage; acute tubular necrosis; coagulopathies; and placental abruption in the mother.
Hemolysis, elevated liver enzyme levels, and low platelets (HELLP) syndrome may be an outcome of severe preeclampsia, although some authors believe it to have an unrelated etiology.
Race
The frequency of mortality differs among race and ethnicity, with African Americans having a worse mortality rate than white women.
Age
Preeclampsia occurs more frequently in women at the extremes of reproductive age.
Clinical
History
Mild-to-moderate preeclampsia may be asymptomatic. Many cases are detected through routine prenatal screening. Patients with severe preeclampsia display end-organ effects and may complain of the following:
- CNS
- Headache
- Visual disturbances - Blurred, scintillating scotomata
- Altered mental status
- Blindness - May be cortical or retinal
- Dyspnea
- Edema: This exists in many pregnant women but sudden increase in edema or facial edema is more concerning for preeclampsia. The edema of preeclampsia occurs by a distinct mechanism that is similar to that of angioneurotic edema.
- Epigastric or right upper quadrant (RUQ) abdominal pain: Hepatic involvement occurs in 10% of women with severe preeclampsia.
- Weakness or malaise: This may be evidence of hemolytic anemia.
Physical
Findings on physical examination may include the following:
- Increased BP compared with the patient's baseline or greater than 140/90 mm Hg
- Altered mental status
- Decreased vision
- Papilledema
- Epigastric or RUQ abdominal tenderness
- Peripheral edema: Edema can be normal in pregnancy, but a sudden increase in edema or swelling of the face is more suggestive of preeclampsia.
- Hyperreflexia or clonus
- Seizures
- Focal neurologic deficit
Causes
- Pregnancy-associated risk factors
- Chromosomal abnormalities
- Hydatidiform mole
- Multifetal pregnancy
- Oocyte donation or donor insemination
- Urinary tract infection
- Maternal-specific risk factors
- Extremes of age
- Black race
- Family history of preeclampsia
- Nulliparity
- Preeclampsia in a previous pregnancy
- Diabetes
- Obesity
- Chronic hypertension
- Renal disease
- Periodontal disease2
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