U.S. Department of Health and Human Services doc Low-Dose Aspirin for the Prevention of Morbidity and Mortality From Preeclampsia: A Systematic Evidence Review for the U.S. Preventive Services Task Force: Evidence Synthesis Number 112

Preeclampsia is a multisystem inflammatory syndrome that is not well understood. It is defined as the onset of hypertension (blood pressure greater than 140/90) and proteinuria during the second half of pregnancy (greater than 20 weeks’ gestation). While the condition can remain mild until delivery, it can also evolve rapidly into severe hypertension, proteinuria, and eclampsia or hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome, with risk of organ and systemic complications and maternal or fetal death. Even when preeclampsia does not proceed to HELLP syndrome or eclampsia, severe preeclampsia can lead to neurological and visual disturbances, epigastric or right upper quadrant pain, pulmonary edema, or cyanosis. The only curative treatment once preeclampsia develops is delivery, with obvious implications for the health of the infant when it occurs preterm. Systems for diagnosing and classifying the severity of disease vary across professional societies and organizations, including the American College of Obstetrics and Gynecology (ACOG), the American Society of Hypertension (ASH), and obstetrics and gynecology professional organizations in the United Kingdom, Canada, New Zealand, and Australia. ACOG defines severe preeclampsia as any case of preeclampsia that includes one or more of the following characteristics: severe hypertension (systolic at or above 160 mm Hg or diastolic at or above 110 mm Hg), severe proteinuria (ACOG: greater than 5 g/24 hours; ASH: greater than 3g/24 hours), severe oliguria (very low urine output), cerebral or visual disturbances (i.e., headache, blurry vision, scotomata), right upper quadrant pain, pulmonary edema or cyanosis, impaired liver function, thrombocytopenia, or fetal growth restriction. Other organizations include the timing of onset (<35 weeks), nausea or vomiting, and chest pain or dyspnea among diagnostic criteria for severe preeclampsia. Severe preeclampsia can also be retrospectively diagnosed after the occurrence of major maternal or fetal morbidity. Other pregnancy-related hypertensive conditions overlap and can co-occur with preeclampsia. Chronic hypertension, for example, is defined as hypertension predating the pregnancy and/or continuing beyond 12 weeks postpartum. Women with chronic hypertension are diagnosed with superimposed preeclampsia if proteinuria develops after 20 weeks’ gestation. Pregnant women who develop hypertension during pregnancy (without proteinuria) that subsides within 12 weeks postpartum are defined as having gestational hypertension. Women can also develop atypical preeclampsia, in which they have only proteinuria or hypertension coupled with systemic manifestations or preeclampsia occurs before 20 weeks’ gestation or more than 48 hours postpartum. Physicians have used the concept of early- and late-onset preeclampsia to define different manifestations of the syndrome. This concept also allows providers to distinguish between cases developing before 34 weeks’ gestation (less than 35 weeks’ gestation according to ASH) and those developing later. This is important, as research has identified differences in the origins and outcomes of early-onset preeclampsia, which is thought to be related to aberrations in the placentation process. Later-onset disease, on the other hand, is thought to be associated with maternal constitutional and environmental factors, such as multiple pregnancies, high body mass index (BMI), comorbidities, and chronic hypertension. Early-onset preeclampsia is associated with more severe maternal and fetal outcomes.