Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease there may be red blood cell breakdown, a low blood platelet count, impaired liver function, kidney dysfunction, swelling, shortness of breath due to fluid in the lungs, or visual disturbances. Pre-eclampsia increases the risk of undesirable as well as lethal outcomes for both the mother and the fetus including preterm labour. If left untreated, it may result in seizures at which point it is known as eclampsia.

Risk factors for pre-eclampsia include obesity, prior hypertension, older age, and diabetes mellitus. It is also more frequent in a woman's first pregnancy and if she is carrying twins. The underlying mechanisms are complex and involve abnormal formation of blood vessels in the placenta amongst other factors. Most cases are diagnosed before delivery, and may be categorized depending on the gestational week at delivery. Commonly, pre-eclampsia continues into the period after delivery, then known as postpartum pre-eclampsia. Rarely, pre-eclampsia may begin in the period after delivery. While historically both high blood pressure and protein in the urine were required to make the diagnosis, some definitions also include those with hypertension and any associated organ dysfunction. Blood pressure is defined as high when it is greater than 140 mmHg systolic or 90 mmHg diastolic at two separate times, more than four hours apart in a woman after twenty weeks of pregnancy. Pre-eclampsia is routinely screened during prenatal care.

Recommendations for prevention include: aspirin in those at high risk, calcium supplementation in areas with low intake, and treatment of prior hypertension with medications. In those with pre-eclampsia, delivery of the baby and placenta is an effective treatment but full recovery can take days or weeks. When delivery becomes recommended depends on how severe the pre-eclampsia and how far along in pregnancy a woman is. Blood pressure medication, such as labetalol and methyldopa, may be used to improve the mother's condition before delivery. Magnesium sulfate may be used to prevent eclampsia in those with severe disease. Bed rest and salt intake have not been found to be useful for either treatment or prevention.

Pre-eclampsia affects 2–8% of pregnancies worldwide. Hypertensive disorders of pregnancy (which include pre-eclampsia) are one of the most common causes of death due to pregnancy. They resulted in 46,900 deaths in 2015. Pre-eclampsia usually occurs after 32 weeks; however, if it occurs earlier it is associated with worse outcomes. Women who have had pre-eclampsia are at increased risk of high blood pressure, heart disease and stroke later in life. Further, those with pre-eclampsia may have a lower risk of breast cancer.