1. The purpose of this study was to determine whether the 24 h urinary
albumin excretory rate was increased in the third trimester of normal
pregnancy or in pregnant women with hypertension who had 24 h urinary
total protein excretion within the normal range. 2. Twenty-four hour
urinary creatinine and albumin excretions were determined prospectivel
y in 26 nonpregnant and 115 pregnant women in their third trimester (4
0 in normal pregnancy, 38 with mild preeclampsia, 20 with severe pre-e
clampsia, 17 with essential hypertension) in whom urinary total protei
n excretion was normal. Both the urinary albumin excretion rate and th
e urinary albumin/creatinine ratio were compared among the groups. The
clearance of albumin relative to that of creatinine was also calculat
ed in the hypertensive women and in 14 of the non-pregnant women and n
ine of the normal pregnant women. 3. The twenty-four hour urinary albu
min excretion Fate was similar in non-pregnant [8(5-10) mg/day; median
(interquartile range)] and normal pregnant [7(6-10) mg/day] women. Wo
men with essential hypertension [6(4-16) mg/day] and mild preeclampsia
[7(4-10) mg/day] had a urinary albumin excretion rate similar to that
of normal pregnant women. Women with severe pre-eclampsia had an urin
ary albumin excretion rate increased [13(7-32) mg/day] compared with o
ther groups (P<0.05). The clearance of albumin relative to that of cre
atinine was elevated significantly only in women with severe pre-eclam
psia compared with normal pregnant women (0.00054 versus 0.00012; P<0.
05). Blood pressures were similar among all hypertensive groups. The u
pper limit of the urinary albumin excretion rate was 20 mg/day in norm
al pregnant women, similar to that in non-pregnant women. 4. Urinary a
lbumin excretion is unchanged in the third trimester of normal pregnan
cy, but is increased in women with features of severe pre-eclampsia wh
o have normal total urinary protein excretion. This is not fully expla
ined by a reduction in glomerular filtration rate nor by different sys
temic blood pressures, and probably reflects enhanced glomerular capil
lary permeability, possibly with altered maximum renal tubular reabsor
ption capacity for albumin.