Why does pre-eclampsia cause swelling in pregnancy?

Pre-eclampsia can change the lining of small blood vessels and the balance that keeps fluid inside them. Fluid may then collect in tissues, causing puffiness. Swelling can affect the hands, face, feet or ankles. Mild ankle swelling can also happen in an uncomplicated pregnancy, particularly after standing, so appearance alone cannot determine the cause.

Swelling that appears suddenly, becomes marked, or affects the face and hands is more concerning when it occurs with headache, vision changes, upper-abdominal pain, breathlessness or feeling unwell. Blood pressure and urine checks help clinicians assess the wider picture.

Tell your midwife or obstetric clinician about new or rapidly increasing swelling, especially in your face or hands. Mention when it began, whether one leg is more swollen, and any headache, visual symptoms or abdominal pain. Keep scheduled blood-pressure checks and take prescribed medicines exactly as directed.

For ordinary dependent swelling, resting with your feet raised, changing position regularly and avoiding prolonged standing may help. Do not take water tablets or restrict fluids unless your maternity clinician specifically advises it.

Seek urgent maternity assessment for sudden swelling with severe headache, vision changes, severe upper-abdominal pain, breathlessness, chest pain, fainting, confusion or reduced fetal movement. One-sided leg swelling with pain or breathlessness also needs urgent assessment because it may have a cause unrelated to pre-eclampsia.

Ask: Is this pattern of swelling expected for my stage of pregnancy? What are my blood-pressure and urine results? Should I monitor swelling or symptoms at home? Which changes require same-day review?