During normal pregnancy total body water increases by 6 to 8 liters, 4 to 6 liters of which are extracellular, of which at least 2 to 3 liters are interstitial. At some stage in pregnancy 8 out of 10 women have demonstrable clinical edema. There is also cumulative retention of about 950 mmol of sodium distributed between the maternal extracellular compartments and the product of conception. Thus, changes in factors governing renal sodium and water handling accompany alterations in local Starling forces whereby there is a moderate fall in interstitial fluid colloid osmotic pressure (COPi) and a rise in capillary hydrostatic pressure (Pc), as well as changes in hydration of connective tissue ground substance. Edema is a traditional criterion for diagnosing pre-eclampsia, but should no longer be used as its detection is not clinically useful. The role of diuretics in obstetric practice should be restricted to the management of pulmonary edema in pre-eclampsia. Volume expansion therapy in pregnancy runs the risk of pulmonary or cerebral edema, particularly in the immediate puerperium. Vulval edema and erythematous edema associated with deep venous thrombosis are rare but dangerous complications of pregnancy.