Pre-eclampsia is a pregnancy-related disorder characterised primarily by newly developed high blood pressure and evidence of organ involvement, classically including protein in the urine. It usually develops from 20 weeks of pregnancy onwards, although it can occur earlier in unusual circumstances and can also develop after the baby has been born. The condition can range from mild disease requiring monitoring to severe disease capable of causing life-threatening complications for the pregnant person and serious consequences for the fetus. It is not simply ordinary pregnancy-related high blood pressure: pre-eclampsia involves a broader disturbance affecting maternal organs and placental function. Regular antenatal blood-pressure and urine checks are therefore important because the earliest signs may produce no symptoms that the pregnant person can recognise.
The precise cause of pre-eclampsia is not completely understood. Current understanding places an important role on abnormal development or function of the placenta and disturbances in the maternal vascular system, with consequences for blood vessels and multiple organs. The placenta normally develops an extensive blood supply to support fetal growth, and abnormalities in placental vascular adaptation can contribute to reduced or dysregulated placental perfusion.
Placental and maternal signalling can then promote widespread endothelial dysfunction, vascular constriction and increased blood pressure, while organs such as the kidneys, liver and brain can become affected. The condition is therefore not caused simply by stress, salt intake or ordinary pregnancy swelling. Its biology involves complex interactions among placental development, maternal cardiovascular responses, immune mechanisms and genetic and environmental factors. The NHS states that the exact cause remains unknown, despite recognised risk factors.
Pre-eclampsia can affect the kidneys, liver, brain, blood vessels and placenta. Renal involvement can result in protein leaking into urine, while hepatic involvement can produce pain beneath the ribs and abnormal liver tests. Vascular and neurological effects can produce severe headache, visual disturbances or, in severe cases, seizures. Abnormal placental function can impair fetal growth and increase the likelihood of premature birth. A particularly severe complication is HELLP syndrome, involving haemolysis, elevated liver enzymes and low platelet count. Severe hypertension also increases the risk of stroke. These complications explain why pre-eclampsia is treated as an obstetric condition requiring structured surveillance rather than as a minor variation in blood pressure.
Several factors increase the likelihood of developing pre-eclampsia. NHS guidance identifies previous pre-eclampsia, chronic hypertension, diabetes, kidney disease, autoimmune disorders such as lupus or antiphospholipid syndrome, multiple pregnancy, first pregnancy, maternal age of 40 or above, a body mass index of 35 or above before pregnancy, a family history and a long interval since a previous pregnancy among recognised risk factors.
These factors do not mean that pre-eclampsia will necessarily occur; they alter statistical risk and influence how closely someone may be monitored. The combination of several risk factors can be particularly important when clinicians decide whether preventive measures such as low-dose aspirin should be considered. Risk assessment is therefore an important part of antenatal care.
Diagnosis involves more than a single blood-pressure measurement. Antenatal care routinely includes blood-pressure checks and urine testing, and suspected pre-eclampsia may lead to additional blood tests and ultrasound assessment of fetal growth. Clinicians may measure platelet count, kidney function and liver enzymes and assess fetal growth, placental function and amniotic fluid according to the clinical situation. Some people have significant disease with few or no symptoms, which is why routine appointments matter. Conversely, pregnancy can cause headaches, swelling and other symptoms for reasons unrelated to pre-eclampsia, so symptoms must be interpreted alongside objective measurements and examination rather than treated as diagnostic by themselves.
There is currently no medication that permanently removes the underlying condition while the pregnancy continues; delivery of the placenta is ultimately what causes pre-eclampsia to resolve, although symptoms and complications may persist for a period after birth. Management is based on severity and gestational age and may include closer maternal and fetal monitoring, antihypertensive medication to control blood pressure and medication such as magnesium sulfate when seizure prevention is necessary.
If continuing the pregnancy becomes more dangerous than delivering the baby, clinicians may recommend induction of labour or caesarean birth depending on circumstances. When early delivery is anticipated, treatments such as corticosteroids may be considered to improve fetal lung maturity. The appropriate balance between prolonging pregnancy and delivering safely requires specialist obstetric assessment.
Pre-eclampsia can also occur after delivery, sometimes days or weeks postpartum, which is why severe headache, visual disturbance, sudden swelling, upper abdominal pain, vomiting or feeling very unwell after birth should not automatically be attributed to normal recovery. Postpartum pre-eclampsia can require urgent assessment and treatment even if blood pressure was normal during pregnancy. The NHS advises urgent medical help for symptoms suggestive of pre-eclampsia during pregnancy or in the weeks following birth. This distinction is important because delivery does not instantly eliminate all maternal vascular and inflammatory abnormalities, and severe complications such as seizures can occur after the baby has been born.
Prevention and risk reduction focus on antenatal surveillance and, for people at sufficiently high risk, clinician-directed interventions. NHS guidance states that low-dose aspirin from around week 12 until birth may be prescribed for people assessed as being at increased risk, and calcium supplementation may be advised when dietary calcium intake is inadequate. Neither should be started independently without medical advice because the indication and dose depend on individual circumstances.
A healthy balanced diet, appropriate physical activity and maintaining a healthy weight are beneficial for general pregnancy health but cannot guarantee prevention. The essential distinction is that pre-eclampsia is a potentially serious pregnancy complication involving hypertension and systemic effects, and early detection through antenatal care is central to reducing complications.
