1. family and parenting
2. motherhood
3. pregnancy

Total body water in pregnancy:
bioelectrical
impedance1
assessment
Henry
and
C Lukaski,
William
ABSTRACT
culated
dance
Determinations
during,
and
after
once in a group
in another
group
TBW
creased
postpartum.
partum
pregnant
calculated
women
increased
or changes
These
findings
model.
practical
and
valid
method
KEY
WORDS
pregnancy
more
body
different
predicted
indicate
Am J Cli,,
pregnancy,
and
depostand
in
of the variance
in preweight,
abdominal
cir-
vs 4-50%,
nonpregnancy
than
either
the
for determining
measured
impedance
method
is a
longitudinal
changes
1994;59:578-85.
body
water,
bioelectrical
impedance,
accepted
is necessary
that
that
components
nents
include
the
changes
of weight
gain
the products
fluid),
maternal
for proper
tus (1). The development
weight
gain during
pregnancy,
amniotic
uterine
and
weight
gestational
of
standards
however,
in the
during
preg-
of the fe-
for optimal
maternal
has been limited
by the
relative
are not well
of conception
breast
gain
development
contribution
defined.
(fetus,
tissue,
of the
These
compoplacenta,
and
body
water
affecting
the interpretation
of individual
weight
topic
of changes
in maternal
body
composition
pregnancy
the limited
in healthy
available
women
has
information,
been reviewed
it was concluded
mains
a need to determine
the effects
position
on the outcome
of pregnancy.
regarding
the use of available
of pregnant
can
nancy
578
women,
be performed
deuterium
or
and
ids were
safely
by using
oxygen-18.
postpartum
to assess
of total
isotope
Investigations
have
been
gain.
during
Because
that there
of changes
in body
Although
limitations
methods
determination
(2).
limited
body
body
of
recomexist
fat content
water
(TBW)
dilution
methods
with
of TBW
during
preg-
generally
to cross-sec-
Am
J Clin
Nutr
with an emphasis
on the final weeks
of pregnancy
determinations
of TBW
made before
pregnancy.
different
experimental
methods
and biological
flu-
used
in the determination
of isotope
dilution
volumes.
One approach
that may facilitate
large-scale
studies
of TBW
in pregnant
women
is tetrapolar
bioelectricah
impedance
analysis
(BIA).
This
method
relies
on the conduction
of a single-frequency,
constant
electrical
current
to determine
total
conductor
volume of the body (9). Because
water
and electrolytes
are the
dominant
factors
affecting
electrical
conduction
in the body,
TBW is easily
demonstrated
lenge
assessed
by tetrapolar
BIA (10). Previous
the validity
of this approach
to estimate
for any
changes
noninvasive
in water
values
reported
to influence
rent
21).
(20,
also
application
is limited
pregnancy
conductivity
volume
hematocrit
objective
and
change
of this method
in
(17-19).
represents
a chal-
technique.
distribution,
research
TBW
in
body
In addition
geometry
to
and
(1). Each of these factors
has been
of an applied
electrical
cur-
the conduction
1994;59:578-85.
to develop
and validate
a model
by using
TBW
during
pregnancy.
This
study
the practicality
and validity
of using BIA to monchanges
in TBW.
BIA variables
demonstrates
itor longitudinal
was
to predict
Methods
Subjects
Initially,
(intracel-
lular and extracehiular
water),
and maternal
fat. They change
in
variable
amounts
among
women
during
pregnancy,
thereby
distinctly
The
studies
without
Furthermore,
(3-8)
second
It is widely
recognition
tional
The purpose
of the present
study was to determine
longitudinal
changes
in TBW in a series
of women
before
conception,
periodically
throughout
pregnancy,
and in the postpartum
period.
A
Introduction
nancy
B Hall
adults and children
(11-16).
The
conditions
of changing
fluid status
Assessment
of TBW
in human
respectively).
impedance
with the pregnancy
that the impedance
Nutr
Total
then
in pregnancy
(50-75%
with the
significantly
in TBW.
were
derived
from nonpregnant
to measured
values.
Changes
explained
than did
or hematocrit
in TBW
estimated
were
cal-
measurements
during
of TBW
with models
were similar
changes
(113W)
and bioelectrical-impein a group of 15 women
Similar
significantly
Estimates
model
water
Clinton
of 50 nonpregnant
women
and intermitof 10 women
during
pregnancy
and post-
reactance
and resistance
dicting
changes
in TBW
cumference,
Changes
body
spaces
serially
pregnancy.
J Nielsen,
dinal
nant,
40 women
pregnancy
an inability
volunteered
study.
Because
to meet testing
to participate
of difficulty
schedules,
in the
in becoming
and personal
longitupregconsid-
From the United States Department
of Agriculture,
Agricultural
ReService, Grand Forks Human Nutrition
Research
Center, Grand
Forks, ND 58202.
2 Mention
of a trademark
or proprietary
product does not constitute
a
guarantee
or warranty
of the product by the US Department
of Agriculhire
and does not imply its approval
to the exclusion
of other products
that may also be suitable.
3 Address
reprint requests
to HC Lukaski,
USDA, ARS, GFHNRC,
PG Box 9034, Grand Forks, ND 58202-9034.
Received
May 28, 1993.
Accepted
for publication
September
9, 1993.
1
search
Printed
in USA.
C 1994
American
Society
for Clinical
Nutrition
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
partum.
Emily
of total
from deuterium
dilution
measurements
were made
before,
made
tently
A Skiers,
by using
BIA
erations,
subjects
only
gave
the study,
15 women
completed
all aspects
written
informed
consent
before
which
was
Institutional
Review
ture
Study
Human
approved
these
while
gle healthy
infants
not
additional
pregnant
planning
were
pregnancy
and
aged
studied
to develop
The
a pregnancy-specific
Cambridge,
tory,
deuterium
and
y, who
After
vacuum
was
sublimation,
(23). The analytical
and
the 4-h
was repeated
period.
The
space
to participate
study
were
to as
DDS
(D2O
-
y, was
their
were
studied
TBW
pregnancies
used
(in L) was
estimation
exchange
to develop
(DDS),
anthropometry,
and
BIA
the women
baseline
every
90 d unless
a woman
testing
included
determination
testing
in
that
activity
to be
within
the
time based
on her usual
experience,
she underwent
test. If the test was positive,
the woman
was scheduled
to repeat
the
tween
baseline
the time
composition
made before
36-38
The
after
testing
approximately
of the last
evaluation.
pregnancy,
In general,
the women
wk of gestation.
women
were scheduled
delivery.
testing
partum
Each
when
Because
woman
women
received
medical
testing
occurred.
unable
to attend
and postpartum,
a pregnancy-specific
trimester
from
an
stadiometer
cumference,
izontal
overnight
standing
height
DDS
the
body
and a calibrated
measured
with
distance
around
terminations
of DDS
metric
measurements
Total
fast
and
body
was
10-
the
women
weight
scale,
a steel
testing
at 8 wk
clearance
before
abdomen
12 g D2O
as described
to the
were
determined
after
(99.8%
purity;
Each
Cambridge
ingestion.
Plasma
instrumentation
FL).
value
blood
sodium
443; Instrumentation
standard
method
and
Electronics,
Hialeah,
value
was
(Coulter
was
were deobtained
assayed
by
Laboratory,
determined
by
model
a
S; Coulter
with
(22).
Dc-
the
anthropo-
woman
received
Isotope
Labora-
impedance
of
resistance
made
(R)
of nonconductive
reactance
materials.
(Xc)
Aluminum
Products,
surfaces
were
foil
spot
Dallas)
were
posiof the hands and feet
to the metacarpal-phalangealand
detecting
a
and
plethysmograph
(model
101;
as described
elsewhere
(11).
shoes or socks, was supine
on
metatarsal-phalangeal
respectively,
and also medially
between
the distal promiof the radius
and the nina and between
the medial
and
malleohi
at the ankle.
Specifically,
the proximal
edge of
one detector
electrode
ulnar tuberche
at the
laboratory
Abdominal
cirdefined
as the hor-
at the umbilicus
(13).
a 4% over-
of deuterium-hydrogen
= DDS/1.04
(model
Hematocrit
proximal
dates
water
determined
by assuming
concentration
and hematocrit
an aliquot
of the fasting
venous
the deuterium
joints,
nences
lateral
cross-sectional
model
to predict
came
and BIA were made
on the same day.
D20 in urine)
DO)
DDS
electrodes
(no. M6001;
Contact
tioned
in the middle
of the dorsal
postwere
all testing
their
respectively.
tape, was
dose(ing)
(in g/L):
because
made with a tetrapolar
impedance
RJL Systems,
Mt Clemens,
MI)
Each woman,
clothed
but without
assessment.
After
orally
from
DDS
using flame photometry
Inc, Lexington,
MA).
Determinations
body
Protocol
where
sodium
by using
Bioelectrical
chorionic
period
be-
TBW.
The distribution
of observations
was five at 12 wk, eight
at 24 wk, eight at 36
wk gestation,
and nine at 8-10
wk postpartum.
All of the 10 women
underwent
prepregnancy
body composition
deuterium
concentration
90 d. Preg-
women
were tested
at 10 wk
conflicts.
All of the women
were
during
their pregnancies
data were used to develop
first
a
in addition
to measurements
were studied
at
14, 26, and
postpartum
the postpartum
some
and
for
analyzed
spectroscopy
chemistry
a table
was performed.
Two
because
of scheduling
lactating
every
a positive
plasma
human
there was a 14-16-wk
prepregnancy
Clinical
before
measurements.
expected
pregnancy
documented
with
test. On average,
were
were 2.5% (23). DDS
the retained
calculated
of TBW
(24):
Plasma
termined
missed
a menstrual
of deuterium
dilution
All of the women
reported
their usual menstrual
a 26-40-d
cycle.
If a woman
failed
to menstruate
nancy was
gonatropin
water
assessment.
in this study,
for
the
and accuracy
dose given
(4-h plasma
-
for TBW
scheduled
and urine
during
concentration.
electrode
was
wrist,
was
in line with the proximal
and the proximal
edge
in line
with
the medial
edge of the
of the other
malleolus
of the
anlde.
mum
paired
The current-introducing
electrodes
were placed
a minidistance
of the diameter
of the wrist or ankle beyond
the
detector
electrode.
A thin layer of electrolyte
gel was ap-
plied
tation
to each
current
electrode
before
of 800 A, AC,
volunteer
at the distal
drop across the patient
Measurements
the right
variability
the same
hand
was
to the skin.
introduced
electrodes
of the hand and foot;
was detected
with the proximal
of R and
Xc were
and
3-4
h after
ingestion
R and
Xc
measurements
foot,
of repeated
day
application
at 50 kHz
was
<
Statistical
analyses
Data
variables
are expressed
and physical
made
by placing
An cxciinto the
the voltage
electrodes.
electrodes
of deuterium.
determined
on
The
on
1 l.
as mean
± SE.
characteristics
Models
to predict
using
TBW
impedance
were
de-
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
volunteering
longitudinal
excreted
deuterium
of
hourly
infrared
deuterium
TBW
After
obtained
by fixed-filter
by using
plasma
in a subsample
were
All urine
for
plasma
precision
calculated
distilled-deionized
tested
samples
analyzed
concentrations
mL
was
plasma
of the tracer.
period
Design
the
300
obtained
before
and 4 h after
Confirmation
of equilibration
concentration
ingestion
for deuterium
and
is referred
during
data
healthy
with
for the prediction
sample
group.
aged 22-35
model
sin-
mixed
whom
from
5)
equilibration
is termed
were
a model
This
BIA
=
(in L) was
cross-sectionally
TBW
group
(n
for 4 h after
All of
MA)
water.
Venous
blood samples
were
ingestion
of the deuterium
mixture.
of plasma
aged
re-
and delivered
This
22-35
impedance
were
pregnant.
pregnancies
women,
and
postpartum.
Dakota
of Agricul-
4 multigravidae,
study.
They
to become
full-term
of TBW by using
BLA variables.
the nonpregnant
model-development
Another
group of 10 primigravidae,
before
All
in
women
without
complications.
cross-validation
sample.
the longitudinal,
Fifty
were
had normal
579
PREGNANCY
Committee.
they
women
ofNorth
and the US Department
Fifteen
women,
1 1 primigravidae
and
21-37
y, participated
in the longitudinal
cruited
of the study.
participation
by the University
Board
AND
LUKASKI
580
TABLE!
Prepregnancy
the women
sample5
AL
Results
physical,
hematologic,
and bioelectrical
in the model groups and the longitudinal
characteristics
validation
of
The
and
Model
29.3
168.2
62.9
22.3
31.5
Age (y)
Height (cm)
Weight (kg)
Body mass indext
Body
water (kg)
Water wI/body weight
(%)
Resistance
(CI)
Reactance
(rh)
28.7
167.4
63.8
± 1.2
±
578
167.4
± 2.0
Table
± 1.8
3.0
general
0.9
±
22.7
± 1.33
22.4
± 1.2
0.7
30.3
±
1.2
31.8
± 1.0
± 0.9
50.2
± 1.7
50.4
±
± 0.01
0.41
± 0.02
±
±
±
0.42
12
64 ± 4
141
± 2
586
± 8
66
± 2
1.9
140 ± 2
594 ± 15
71
± 2
analysis
(25) in the nonpregnant
were evaluated
in the
with
the
maxi-
and pregnant
women.
longitudinal
study group
to determine
the validity
of the nonpregnancy
and pregnancy
BLA
models
to predict
measured
TBW (26). Measured
and predicted
TBW values
determined
analysis
of variance
with
of physical
parisons
longitudinally
were
a repeated-measures
characteristics
were
compared
design
done
with
by using
(25). Coma one-way
analysis
of variance
(25). When
the main effect was significant,
post hoc Tukey’s
contrasts
were used to identify
significant
differences
(25). The method
of Bland
and Altman
(27) was used
to determine
bias in the prediction
of TBW and changes
in TBW
with impedance
measurements.
TABLE
Plasma
2
deuterium
2 shows
oxide
(D2O) concentrations
and changes
during
plasma
plasma
deuterium
data, during
pattern
did
plateau
was
or
in each
model
L There
bioelectrical
are no
impedance
deuterium
concentrations
and
values
during
the deuand after pregnancy.
In
concentration
reached
a plateau,
at rs3
de-
in deuterium
condeuterium
concen-
the remainder
of the equilibration
not change
until the third trimester
established
the postpartum
h. Equilibration
test,
when
occurred
at 2
the
at 2 h in
period.
Longitudinal
changes
pattern
impedance
during
was
pregnancy
observed
characteristics
for the physical,
measured
biochemical,
longitudinally
during
pregnancy
(Table 3). Body weight
and abdominal
circumference
increased
significantly
after the first trimester
and did not return
to prepregnancy
status
in the postpartum
period.
Body mass indcx increased
Body water
significantly
during
increased
significantly,
significantly
creased
matocrit
during
the second
whereas
pregnancy;
TBW
and third trimesters.
R and Xc decreased
decreased,
R and
Xc
in-
significantly
postpartum,
returning
to control
values.
Hevalue decreased
significantly
during
pregnancy
then reto prepregnancy
turned
values
was no significant
change
weight
during
pregnancy
Predictors
oftotal
Some
nificantly
body
in the
postpartum
in TBW expressed
and postpartum.
period.
There
as a fraction
of body
water
physical
and impedance
variables
were
with TBW
in the nonpregnant
women
test and by pie gnancy
deuteri um equilibration
Time
correlated
sigand the women
status5
after oral D20 dose
2h
lht
Oh
the
tration
h. This
and
stepwise-multiple-regression
in Table
3h
4h
gIL
0.03
Prepregnancy
± 0.01
First trimester
Second
0.04
trimester
± 0.01
0.03
±
0.01
0.03
± 0.01
1
Third
2.33
3.51
± 0.12
76±4
L
trimester
57±3
2.11 ± 0.13
69±4
2.06
2.52
2.33
± 0.14
± 0.15
0.03
± 0.01
2.30
± 0.14
112±4
76±5
f±
SE;n = 5.
t Change significantly
different
at 1 h than at other times, P < 0.05 (Tukey’s
contrasts).
:1:Prepregnancy
significantly
different
from other time periods, P < 0.001.
§ Calculated
as ratio of timed postdose
concentration
to baseline (0 h) D20 concentration.
II Significantly
I
Significantly
different
different
from 2-, 3-, and 4-h concentration
for third trimester,
from 3- and 4-h concentration
for third trimester,
P
± 0.14
83±51
3.40 ± 0.12
68±511
Postpartum
L
± 0.16
116±5
3.48 ± 0.13
86±4
3.11 ± 0.13
99±5
P <
<
0.05.
0.05.
3.52
± 0.15
116±5
3.50
± 0.15
116±5
86±3
3.12 ± 0.12
103±4
± 0.13
86±3
3.11 ± 0.13
99±5
2.80
2.81
3.46
± 0.14
± 0.13
92±4
3.41
113±4
± 0.12
3.46
± 0.14
93±5
3.40
±
112±4
0.13
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
by
of the women
summarized
relative
to the preadministration
equilibration
tests before,
during,
A general
t In kglm2.
mum R2 method
These
models
are
fined as a significant
increase
in the change
centration
relative
to the baseline
or predose
1 ± SE.
rived
characteristics
sample
equilibration
changes
terium
±
63.0
0.43 ± 0.03
140 ± 2
(mmollL)
28.5
0.7
±
Isotope
(n=15)
1.5
±
50.4
Hematocrit
(I)
Plasma sodium
0.5
1.4
1.7
±
Validation
group
Pregnant
(n=10)
(n=50)
prepregnancy
validation
marked
differences
in the physical
characteristics
among
the groups.
groups
Nonpregnant
5
ET
BIA
TABLE 3
Characteristics
of 15 women
before,
during,
Weight (kg)
Body mass indext
C, (cm)
Hematocrit
(I)
Plasma sodium (mmol/L)
Resistance
()
Reactance
(Cl)
Body
water (kg)
Water wt/body wt (%)
S
SE. Values
,
PREGNANCY
581
and after pregnancy5
Prepregnancy
First
63.0
22.4
76.1
0.41
140
Second
trimester
trimester
Third
trimester
Postpartum
± 3.0
64.0
± 2.9&
71.6
±
2.9l
773
±
3.2c
68.!
± 2.9
± 1.2
22.9
± 1.2’
25.6
± 12’
27.6
± 1.3L
23.6
± 0.9’
± 2.9’
80.7 ± 2.7’
94.5
± 2.6k’
102.9
2.5c
90.0
± 2#{149}2b
± O.021)
0.37
±
006*bc
0.35
± O.08c
0.36
140
±
2
589
± 16’
2
±
594 ± 15’
71 ± 2
31.8 ± 1.0’
50.4 ± 1.9
in the same
AND
± O.08c
0.40
± 0.08’
14!
± 2
142
± 2
141
551
± 18”
52!
± 24C
573 ±
69 ± 2
row with different
±
63 ±
59 ± 2C
2b
± 2
67
19.b
±
2”
1#{149}2b
32.5
± 1.0’
35.1
± 1.0”
39.6
± !.6c
34.2
±
51.1
±
49.5
±
1.6
50.0
± 1.4
50.3
± 1.5
superscripts
1.5
are significantly
different,
0.05 (Tukey’s
P <
contrasts).
t In kglm2.
:: Abdominal
circumference.
during
pregnancy
and postpartum
(Table
was a relatively
weak,
though
significant,
studied
longitudinally
4). Standing
height
of TBW.
of TBW,
predicting
TBW.
Regardless
accounting
Xc,
of status,
R was the best single
for 67-79%
of the variance
in
hematocrit
value,
and
abdominal
SEE = 1.15, P < 0.0001)
to the measured
equation
y = 0.990x
+ 0.42 has a slope
circum-
an intercept
ference
explained
more of the variance
in predicting
TBW in the
pregnant
than in the nonpregnant
women
(61%,
24%, and 16%
in comparison
with 12%, 10%, and < 1%, respectively).
tween
Prediction
model
cated
With
The
multiple-regression
equations
derived
separately
for
and
ht/R,
and
women.
of TBW
abdominal
in
circumference,
the
pregnant
women
include
body
weight,
hematocrit
value,
the
correlated
derived
from
of TBW
nant women
ilar to those
Analyses
TBW
by using
of the prediction
BIA
models
in nonpregnant
(Table
5) yielded
mean TBW values
determined
by using isotope
dilution
of the relationships
among
measured
values
indicated
pregnancy
model,
(R2
0.893,
SEE
linear
predicted
=
1.46,
relationships.
TBW
P <
was
(Table
and
By
using
correlated
0.0001)
with
were
ofchange
the
A
non-
significantly
measured
TBW.
The regression
equation
relating
measured
and predicted
TBW
values,
y = 0.958x
+ 1.15, has a slope similar
to 1 and an inter-
TABLE 4
Predictors
of total b ody water
Nonpregnant
Pregnantjl
S
Abdominal
tP
<
0.05.
:l:P
<
§P
<
0.0005.
0.0001.
IIUnivariate
in 50 non pregnant
women
and
predicted
with either
prediction
the residual
scores
were
0.028)
=
The
was
TBW
mean
were
the average
bevalues)
values
TBW
weakly
mdimodel.
not sig-
values.
Also,
TBW
values
and predicted
model
with
R
and
Xc
(Table
correlated
TBW
values.
best
TBW
good
predictors
of
explained
than
did
(49%,
value
predictor
which
were
7). They
in estimating
ht/R,
with
the measured
differences
residual
(R2
weight,
27%,
longitudinal
accounted
for
of
more
and
TBW
(cu6O%)
abdominal
8%,
respec-
determinations
90%
of the
of
variance
in
TBW.
similar
pattern
was
observed
in
estimating
longitudinal
changes
R were
in TBW from changes
in these variables.
Changes
in ht/
the best predictors
of change
in TBW from prepregnancy
values.
Changes
of change
studied
in R, body
in TBW
thro ughout
than
pregnancy
weight,
were
and Xc were
abdominal
better
circumference
predictors
and
he-
and postpartum
Height
Weight
Resistance
Reactance
Hematocrit
C,,,5
0.331t
O.250t
O.580j
O.614f
-O.889
-0.821*
-O.349t
-O.778
O.308t
O.490t
0.028
-O.396t
circumference.
correlations
and 15 women
measured
relationships
model,
or hematocrit
predicting
predicted
(eg,
pregnancy
variance
TBW
6).
the
values
in TBW
measured
tively).
sim-
among
TBW
pregnancy
Predictors
circumference,
and pregthat
the
P = 0.36)
of the
derived
relationships
(R2
= 0.020,
The
values.
The regression
not different
from 1 and
predicted
between
throughout
Use
of the
no significant
the nonpregnancy
the differences
Xc.
Prediction
and
mean
model
pie(R2 = 0.918,
to 0.
of the
measured
nificantly
the
estimation
of TBW
in the 50 nonpregnant
women
and the 10
women
studied
cross-sectionally
during
pregnancy
are presented
in Table
5. The independent
variables
are ht/R and body weight
in the nonpregnant
The
predictors
similar
Examination
pregnancy
related
adjusted
for repeated
measures.
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
predictor
predictor
cept not different
from 0. Similarly,
the
dicted
TBW
values
that were significantly
LUKASKI
582
TABLE 5
Multiple-regression
equations
to predict total body water (TBW)
using bioelectrical
impedance,
anthropometric,
and biochemical
measures
of 50 nonpregnant
women and 10 women studied
intermittently
during pregnancy
and postpartum5
ET
AL
TABLE 7
Relationship
by
measurements,
variables
among impedance,
anthropometric,
biochemical
and total body water (TBW), and changes
in these
before, during, and after pregnancy
in 15 women
TBW
Independent
Nonpregnancy
X2
model:
-
0.029
X4
ing
(86%,
in TBW
72%,
+
+ 0.051
X5
and
and
0.980
0.97
0.901
0.920
0.932
0.949
0.960
1.42
and
with
With
and
the
the
8). In
of change
in TBW.
with the analysis
predicted
changes
postpartum.
63%
(Table
lactation
S
Urnvariate
t
Abdominal
SEE
r5
0.789
2.5
0.860
1.7
0.755
2.7
0.694
2.4
0.950
0.701
0.520
0.282
1.2
3.1
0.910
0.725
1.3
2.3
3.8
0.635
2.8
4.3
0.200
3.5
correlations
SEE
between
predictions
residual
based
in Figure
1. The slope
= 0.051;
P = 0.96)
and
1.07;
measures.
scores
(deuterium
on the impedance
dilution
pregnancy
for individual
changes
in TBW
as a function
of mean
in TBW (deuterium
dilution
and by predicted
impedance)
is shown
=
for repeated
the
of this line is similar
intercept
is not
different
to 0
from
(t
0 (t
P = 0.21).
in
of the
in TBW
nonpregnancy
model)
change
adjusted
circumference.
The relationship
minus impedance
circumference.
estimates
changes
Hematocrit
1.30
1.20
1.07
0.92
underestimated
model
yielded
to the measured
Resistance
Reactance
HeightIResistance
Weight
Cabdt
significantly
is confirmed
measured
and
1.18
X2
as compared
pregnancy
0.963
+ 2.833
69%
rS
0.063
abdominal
model
during
observation
between
pregnancy
-
Xl
0.043
Xc, reactance;
contrast,
the pregnancy
TBW that were similar
This
tionships
Xl
reladurmodel
Discussion
The use of tetrapolar
BIA
new (28). Early investigations
technology
established
to assess
TBW
is not
that tetrapolar
bioehec-
the linear
relationship
between
measured
and predicted
change
in TBW (y = 1.038x
+ 0.881) has an intercept
that is significantly
different
(P < 0.006)
from 0. In contrast,
the pregnancy
model
trical conductance,
expressed
as hR and normalized
tor length
or stature,
was a significant
predictor
healthy
adults and children
(10). Subsequent
studies
estimated
sured
changes
in TBW
(y = 0.998x
+ 0.393);
the slope
and
intercept
of this relationship
were similar
to the line of identity.
Differences
between
measured
and predicted
changes
in TBW
BIA is a valid method
to predict
acute changes
in TBW,
either
in response
to saline infusion
or dehydration
(19, 29). The findings of the present
study indicate
that BIA is a valid approach
to
determine
longitudinal
changes
in TBW,
particularly
in human
determined
nificantly
pregnancy.
An important
The
changes
that
were
with the nonpregnancy
(R2 = 0.10, P < 0.05)
residual
calculated
in TBW
scores
with
from
the
the pregnancy
linearly
with
model
the
measured
were
average
and
model,
(R2
0.03, P = 0.21) to the mean
pregnancy
and postpartum.
related
TABLE 6
Comparisons
among measured
and predicted
15 women studied serially before pregnancy,
pregnancy,
and postpartum5
correlated
sigTBW values.
predicted
however,
TBW
to the mea-
were
values
changes
not related
assessed
during
total body water values in
during each trimester
of
observation
is that
changes
and regional
fluid
of BIA to estimate
accumulation
changes
significantly
in conductor
among
TBW
TBW
measured
and
Predicted
total body
Nonpregnancy
model
L
water
Prepregnancy
First trimester
Second trimester
Third trimester
Postpartum
S
SE. Significant
31.7
±
1.0
32.2
32.2
35.1
38.6
34.0
± 1.0
1.0
1.6
1.1
effect
±
±
±
1.0
31.9
±
32.8
± 1.0
32.4
±
1.0
35.3
38.1
34.0
±
1.1
35.3
±
1.0
± 1.7
38.9
±
1.6
± 1.0
33.6
±
1.0
of time period,
P
<
0.0001.
devel-
water
water
Nonpregnancy
model
Pregnancy
model
kg
L
±
geometry
models
in total body
in total body
Pregnancy
model
L
with
TABLE 8
Comparison
of measured
and predicted
changes
during pregnancy
and lactation
in 15 women5
Measured
Measured
in body
influence
the ability
volume.
Comparisons
predicted
Changes
for conducof TBW
in
showed
that
1.0
First trimester
Second trimester
Third trimester
Postpartum
0.5 ± 0.4
3.5 ± 0.6
7.1 ± 1.1
0.1
± 0.3
0.6
1.7
± 0.3t
3.4
±
5.4
± 1.lt
6.2
± 1.0
2.3
1.2
± O.4t
1.9
± 0.5
± 0.6
± 0.4
0.5
S f
SE. Change measured
relative to prepregnancy
values. Significant effect of both method and time period, P < 0.0001 (ANOVA).
t Significantly
different
from pregnancy
0.05 (Tukey’s contrasts).
P <
model
and measured
values,
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
values
0.700
20%, respectively).
The
nonpregnancy
changes
0.610
=
TBW
Res, resistance;
matocrit
=
TBW
ETBW
SEE
2
+ 0.06
xl, heightIres
X2, weight
Pregnancy
model:
0.069 X3
xl, heightIres
X2, C,,,,,
X3,weight
X4, Xc
X5, hematocrit
5
variable
BIA
4
A
U
.
AND
U
Trimestar
1
32).
.
Trlmsstsr
2
strated
3
by
A TIIm.S$Sr
A
PREGNANCY
.
Post partum
#{149}U
A
#{149}‘#{149}
,
,
I
I
‘
.
A
0
A
.
.
2
4
6
8
Mean change
10
12
14
16
In TBW, kg
=
hence
and
pregnant
subjects
ences among
the mean estimates.
a generalized
model
(eg, either
model)
is capable
of adequately
TBW.
However,
pregnancy
comparisons
values
demonstrated
model
estimated
Therefore,
the
diction
values.
indicated
no differ-
This observation
indicates
that
a nonpregnancy
or pregnancy
estimating
mean
changes
in
of changes
to those
postpartum
(33).
was
impedance
Because
changes
in resistivity
such as hematocrit
electrical
conductor
directly
influences
extracellular
than in nonpregnant
women
suggests
that Xc was indexing
characteristic
observed
in TBW
from
throughout
the pre-
pregnancy
and
that only the pregnancy-specific
prechanges
in TBW similar
to the measured
pregnancy-specific
model
offers
the sen-
of late
(61% vs 12%, respectively),
the increase
in extracehlular
studies
pregnancy.
(3,
6-8)
intermittently
The
ranged
during
gestation,
and TBW observed
in the present
reported
in cross-sectional
studies
reported
from
maternal
9.2
pregnancy.
the range
gestational
If these
of weight
changes
weight
gain
in TBW
is 9.2-13
in these
studies
to
underestimate
pregnancy
This
monitor
and
limitation
of BIA
changes
in regional
cirrhosis
estimates
BIA measurements
altered
fluid status
after
BIA
paracentesis
measurements,
improve
regional
longitudinal
geometry.
of the
(31).
important
value.
during
TBW and 14.3 kg in body weight
with
resenting
50% of the weight
gain.
It is important
to note
that the values
the
change
provided
actually
DDS in these studies(3,
6-8).
DDS, assuming
a 4% deuterium-labile
been
reported
in attempts
accumulation.
In patients
The
was
to
with
suggested
that regional
trunk or abdomen,
may
in TBW
ative
to
There
discussed
of measures
suggested
the present
of TBW
that
of body
(21)
study.
in pregnancy
hematocrit
is based
on
but
geometry
not
for TBW
was
the present
oxygen-18
TBW
before
from
(24),
represent
report
conception,
Ct al (36)
of
during
reported
longitu-
monitor
the dilution
hemat-
nonaqueous
was made
studies
to the
to that
weight
gain
observed
reported
in the
methodologic
and longitudinal
differences
studies.
in the
present
study
between
In contrast
the
to
study and other studies
(3-8),
Forsum
et al (36) used
labeled
water and sampled
saliva rather than blood to
it is recognized
with a bipolar
electrode
system,
volume
or hematocrit
value (20,
were
IfTBW
is calculated
hydrogen
exchange
Forsum
of TBW
is similar
are two important
cross-sectional
imple-
value
could
be an
the findings
that the
and
postpartum.
contribution
of TBW
remains
weight
rep-
before
pregnancy
(61.0
± 2.0 kg) as the women
in the present
study.
The observed
average
gestational
change
in weight
was
1 1.7 kg, which
is similar
to the 14 kg shown
in the present
study.
The mean change
in TBW,
however,
was 5.7 L in comparison
with the 7.2 L found
in the present
study.
Interestingly,
the relSwedish
study
(49% vs 50%).
inclusion
resistivity
of blood,
determined
is dependent
on the packed
cell
and
in
in pregnancy
ranged
dinal
changes
in body
composition
of a group
of 22 healthy
Swedish
women
who had similar
ages (28.7 ± 0.9 y) and weight
BIA method
to assess
changes
Whether
regional
BIA measure-
previously
The hypothesis
predictor
of TBW
in body
pregnancy,
in the pregnancy-dependent
model
was
which is an index, in addition
to height
mented
and validated
until
Another
specific
predictor
ocrit
has
fluid
estimates
One specific
predictor
abdominal
circumference,
models
also
(30, 31). It has been
specifically
of the
ments
will enhance
be demonstrated.
in BIA
in TBW
of change
in TBW derived
from whole-body
and models
derived
in healthy
adults without
have been shown
to underestimate
fluid loss
the sensitivity
fluid retention
of body
changes
postpartum.
The
from 6.3 to 8.5 L. The relative
contribution
of water to the observed
weight
gain was calculated
to be ci70%. Corresponding
data from the present
study are an average
increase
of 7.2 L in
changes
or a ten-
to
kg (2).
model
a bias
studied
data are normalized
gain
derived
indicated
in four
to 1 1.2 kg in women
the TBW
estimates
range about from 6 to 8 L, which
> 60% of the gestational
weight
gain.
In addition
to the present
study,
there
is only one
the nonpregnancy
which
water
pregnancy.
The changes
in body weight
study are consistent
with those
of human
and
may be
in nonpredic-
Xc was shown
to be a unique
As shown
in the present
study,
in predictingTBW
in pregnant
increases
in TBW.
Analyses
of
and predicted
changes
in TBW
dency
value
vol-
water,
sitivity
to monitor
within-subject
differences
between
measured
from
demon-
determined
TBW.
tors of TBW (13, 35). Importantly,
predictor
of extracellular
water.
Xc explained
more of the variance
estimated
in nonpregnant
system
and
measurements,
factors
variables
in predicting
expansion
40-wk
oped
relationship
volume
of the
hydrogen
(24),
in the calculation
(3, 6-8).
isotopically
that deuterium
Furthermore,
labeled
exchanges
no appropriate
of TBW from
it has
water.
to a small
been
Although
degree
shown
that
concentrations
of oxygen-18
measured
in the blood (23,
and deuterium
are similar
37). Thus, it seems unlikely
factors
the reported
completely
explain
with
correction
apparently
DDS in the previous
differences
salivary
to those
that these
in TBW
val-
Downloaded from ajcn.nutrition.org by guest on June 11, 2014
FIG 1. Plot of the individual
changes in total body water (TBW) during pregnancy
and postpartum
calculated
from the estimates
made by
deuterium
dilution minus the corresponding
change predicted
with the
pregnancy
impedance
model as related to the mean change in TBW calculated by using data from deuterium
dilution and the pregnancy
impedance model. The equation
describing
the data is y = 0.lOlx + 0.017; R2
0.03, SEE
1.28 kg.
=
and
positive
cell
thus TBW,
it is reasonable
to suggest
that BIA variables
unique
predictors
of TBW
and its distribution.
Studies
obese and obese adults identified
R and Xc as significant
U
-2
a tetrapolar
volume
:..
UA
packed
It has been shown
that human
pregnancy
is associated
with an
increase
in blood
volume
and a disproportionate
increase
in
plasma
volume
relative
to red cell mass
(34). Because
plasma
U
U
a significant
between
using
ume
A
A
.::
. -.
Recently,
affect impedance
may be important
#{149}A
U
583
584
ues
LUKASKI
among
however,
and the
the
studies
of TBW
and
gestation.
perimental
likely,
2.
studies
in cx-
3.
It is more
that the inconsistency
among
the
cross-sectional
observations
reflects
longitudinal
differences
design.
One complication
of the use of deuterium
TBW in pregnancy
is the lack of demonstration
ibration
in any of the previous
publications.
Seitchik
(4)
administered
deuterium
dilution
to assess
of isotopic
equilIn an early study,
orally
and
collected
h. An equilibration
more
than 17 h in
pregnant
women
was reported.
The observed
hated DDS was only 10% (32 vs 35 L) at 37-40
change
in calcuwk of pregnancy.
deuterium
or a failure
of true
point
is perhaps
the appropriate
women
pared
These
isotopic
are used to determine
Information
about
nancy
is not
volumes
after
In addition,
frequently
with urine
circumstances
equilibration
in the
scribes
ingestion
the time course
of deuterium
subtle,
the equilibration
result
urine
pregnancy.
of deuterium
literature.
The
of plasma
deuterium
during
pregnancy
of deuterium
in the failspecimens
during
present
study
de-
by duration
of
gestation.
Relative
to control,
the stabilization
of plasma
deuterium concentration
is delayed
from 2 to 3 h in the last trimester
of pregnancy.
This finding
suggests
that previous
studies
of deuterium
dilution
in pregnant
women
that used a 3-4-h
equihibration period
for the determination
topic equilibration
in the blood
of DDS
(3, 6-8).
probably
achieved
iso-
It should
be noted that the pregnant
women
in this study did
not suffer
from any significant
disruption
of electrolyte
homeostasis
as would
be seen in conditions
such
as edema
or pre-
This distinction
eclampsia.
lationship
between
is noteworthy
sodium
and
plasma
vivo and in vitro (20, 38).
the influence
of significant
It would
alterations
because
an inverse
R has been observed
be expected,
in plasma
tration
on the estimation
of TBW in human
investigated
in a subsequent
study.
In summary,
the present
study demonstrates
increase
in TBW during
pregnancy
in humans
assessed
with tetrapohar
BIA. This assessment
that
includes
required
BIA
to correct
variables
for changes
and
geometry
estimating
than
changes
in TBW.
9.
10.
11.
12.
13.
14.
15.
16.
17.
be
19.
measurements
associated
with
changes
in
and post-
anthropometric
or biochemical
measurements.
that BLA is a practical
and useful
method
longitudinal
8.
18.
pregnancy.
The BIA variables
reflect
longitudinal
TBW
as it increases
and decreases
during
pregnancy
partum
better
It is concluded
should
that the significant
can be accurately
requires
a model
anthropometric
in body
rein
therefore,
that
sodium
concen-
pregnancy
7.
preg-
concentration
after
(Table
2). Although
is affected
6.
as comwomen
each urine specin the bladder
may
when
DDS in human
the equilibration
available
so that
remaining
inof
The latter
pregnant
urination
pregnant
5.
20.
21.
for
U
We thank T Hoesley
and C Perreault
for technical
assistance.
Our
appreciation
is extended
to the women who so graciously
and dutifully
participated
in this study.
22.
23.
References
1. Hytten FE. Weight gain in pregnancy.
eds. Clinical physiology
in obstetrics.
Publishers,
1980:193-233.
In: Hytten F, Chamberlain
G,
Oxford:
Blackwell
Scientific
24.
AL
National
Academy
of Sciences.
Nutrition
during
pregnancy.
Washington,
DC: National
Academy
Press, 1990:121-36.
Hytten FE, Thomson
AM, Taggart
N. Total body water in normal
pregnancy.
J Obstet Gynaecol
Br Commonw
1966;73:553-61.
Seitchik
J. Total body water and total body density
of pregnant
women. J Obstet Gynecol
1967;29:155-66.
Duffus GM, MacGilhivray
I, Dennis KJ. The relationship
between
baby weight
and changes
in maternal
weight,
total body water,
plasma volume, electrolytes
and proteins and urinary oestriol excretion. J Obstet Gynaecol
Br Commonw
1971;78:97-104.
Emerson
K, Poindexter
EL, Kothari M. Changes in total body composition
during normal
and diabetic
pregnancy.
Obstet Gynecol
1975;45:505-11.
Pipe NGJ,
Smith
T, Halliday
D, Edmonds
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