Changes preceding the development of preeclamptic toxemia.

No differences were found at the 30th week of pregnancy in total body water, serum sodium, potassium, chloride and osmolality, plasma volume, total protein concentration, intravascular protein mass, serum albumin concentration, intravascular albumin mass, and urinary estriol and pregnanediol in 94 primigravidae who remained normotensive, 35 who developed mild preeclampsia, and 23 who developed severe preeclampsia (i.e. hypertension and significant proteinuria in the third trimester). In twin pregnancies no differences were found between 13 primigravidae who remained normotensive and nine who subsequently developed proteinuria and hypertension.