Sodium and volume dysregulation after apparently normal pregnancy is suggested by abnormal levels of atrial natriuretic peptide, renin and aldosterone.

1. Plasma atrial natriuretic peptide (ANP), renin activity, aldosterone, sodium, potassium and serum total protein and albumin during and after 14 normal pregnancies were compared with age-matched controls. 2. None developed toxaemia and all delivered healthy babies. 3. During pregnancy, plasma renin activity and aldosterone were significantly (P less than 0.01) higher and potassium, total protein and albumin significantly lowew (P less than 0.01) than in controls, while ANP was not different from the control level. 4. At 6-13 weeks postpartum, a significant (P less than 0.01) suppression of renin and aldosterone was accompanied by significant (P less than 0.01) elevation of atrial natriuretic peptide when compared with controls. 5. The hormonal changes are consistent with 'effective plasma volume' reduction during pregnancy and persistent volume expansion after pregnancy, perhaps due to a renal glomerular lesion sustained late in pregnancy. In contrast, levels of potassium, total protein and albumin are consistent with haemodilution during pregnancy and its correction postpartum. 6. Measurements available in seven women 40-120 weeks postpartum showed normal renin and aldosterone levels in most, but ANP was still elevated. 7. Pregnancy may have a protracted effect on volume regulation.