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DOI:
10.1542/peds.2005-1417 2006;117;387-395
Pediatrics Doherty
and Peter E. Hartmann Jacqueline
C. Kent, Leon R. Mitoulas, Mark D. Cregan, Donna T. Ramsay, Dorota A. Throughout
the Day Volume
and Frequency of Breastfeedings and Fat Content of Breast Milk This
information is current as of March 28, 2006 http://www.pediatrics.org/cgi/content/full/117/3/e387 located
on the World Wide Web at: The
online version of this article, along with updated information and
services, is rights
reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275. Grove
Village, Illinois, 60007. Copyright © 2006 by the American Academy of
Pediatrics. All and
trademarked by the American Academy of Pediatrics, 141 Northwest Point
Boulevard, Elk publication,
it has been published continuously since 1948. PEDIATRICS is owned,
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is the official journal of the American Academy of Pediatrics. A monthly at
IRCCS Burlo Garofalo on March 28, 2006 www.pediatrics.org
Downloaded from ARTICLE Volume
and Frequency of Breastfeedings and Fat Content
of Breast Milk Throughout the Day Jacqueline
C. Kent, PhDa, Leon R. Mitoulas, PhDa, Mark D. Cregan, PhDa, Donna T.
Ramsay, PhDa, Dorota A. Doherty, PhDb,c, Peter
E. Hartmann, PhDa aDepartment
of Biochemistry and Molecular Biology, Faculty of Life and Physical
Sciences, and bSchool of Women’s and Infants’ Health, The University
of Western Australia,
Crawley, Western Australia, Australia; cWomen and Infants Research
Foundation, Crawley, Western Australia, Australia The
authors have indicated they have no financial relationships relevant to
this article to disclose. ABSTRACT OBJECTIVE.We
aimed to provide information that can be used as a guide to clinicians when
advising breastfeeding mothers on normal lactation with regard to the frequency
and volume of breastfeedings and the fat content of breast milk. METHODS.
Mothers
(71) of infants who were 1 to 6 months of age and exclusively breastfeeding
on demand test-weighed their infants before and after every breastfeeding from
each breast for 24 to 26 hours and collected small milk samples from each
breast each time the infant was weighed. RESULTS.
Infants
breastfed 11 _
3
times in 24 hours (range: 6–18), and a breastfeeding was
76.0 _
12.6
g (range: 0–240 g), which was 67.3 _
7.8%
(range: 0–100%) of
the volume of milk that was available in the breast at the beginning of
the breastfeeding.
Left and right breasts rarely produced the same volume of milk. The volume
of milk consumed by the infant at each breastfeeding depended on whether
the breast that was being suckled was the more or less productive breast, whether
the breastfeeding was unpaired, or whether it was the first or second breast
of paired breastfeedings; the time of day; and whether the infant
breastfed during
the night or not. Night breastfeedings were common and made an important contribution
to the total milk intake. The fat content of the milk was 41.1 _ 7.8
g/L (range: 22.3–61.6 g/L) and was independent of breastfeeding
frequency. There
was no relationship between the number of breastfeedings per day and the 24-hour
milk production of the mothers. CONCLUSIONS.
Breastfed
infants should be encouraged to feed on demand, day and night,
rather than conform to an average that may not be appropriate for the mother-infant
dyad. www.pediatrics.org/cgi/doi/10.1542/ peds.2005-1417 doi:10.1542/peds.2005-1417 Key
Words breastfeeding,
feeding behavior, feeding volumes,
infant feeding, breast milk Abbreviation IQR—interquartile
range Accepted
for publication Sep 19, 2005 Address
correspondence to Jacqueline C. Kent,
PhD, The University of Western Australia, Biochemistry
and Molecular Biology, M310, 35 Stirling
Hwy, Crawley, Western Australia 6009, Australia.
E-mail: jkent@cyllene.uwa.edu.au PEDIATRICS
(ISSN Numbers: Print, 0031-4005; Online,
1098-4275). Copyright©2006 by the American
Academy of Pediatrics PEDIATRICS
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Downloaded from BREASTFEEDING
MOTHERS SHOULD be made aware of the
variability of milk volumes per breastfeeding, the
frequencies of breastfeedings, and the distribution of milk
intake by day and by night of healthy breastfed infants.1 Mothers
among the !Kung hunter-gatherers have been
observed to breastfeed 4 times every hour during the
day and at least once at night.2 In contrast, Cadogan,3 in
his essay to the Governors of the Foundling Hospital (London,
United Kingdom) in 1748 recommended that infants
be suckled only 4 times a day and not at night, because
he considered the night feeding to result in breastfed
infants’ becoming “over fat and bloated.” Relaxation of
the concept of scheduled breastfeeding was first
strongly promoted by Wickes4 in 1953 and subsequently advocated
by community support groups such as
La Leche League and the Australian Breastfeeding Association
that were at the vanguard of the movement back
to breastfeeding in the early 1970s in Western societies.
As a result, infants were breastfed more frequently both
by day and by night. It now is recognized that
breast milk provides the optimal nutrition for infants, and
current recommendations to mothers are that infants
be breastfed “on demand” (according to their appetite)
exclusively for the first 6 months of life.5,6 Bangladeshi
infants have been found to consume half their
daily milk intake between 6 AM and 6 PM.7 Matheny and
Picciano8 in the United States investigated whether measurement
of milk production over a 12-hour period could
be doubled to determine the 24-milk production. Studying
4-week-old infants, they found that more milk was
consumed between 6 AM and 6 PM and less was consumed
between 2 PM and 2 AM. Doubling of either of these
12-hour intakes resulted in significant inaccuracies in
estimation of 24-hour milk consumption. The product of
the volume of 1 or 2 consecutive breastfeedings and the
number of breastfeedings in the period also has been found
to be inaccurate.9 The data of Cregan et al10 showing variation
in the volume and the frequency of breastfeedings over
24 hours for Australian infants also suggest that
these calculations would be inaccurate. However, for
accurate assessment of milk production, the necessity of
a full 24-hour period of measurement of milk intake in
our society for infants between 4 and 26 weeks has not
been determined. A
wide variation in the frequency of breastfeeding has been
recorded in the United States and Sweden in exclusively breastfed
infants.11,12 These authors collected longitudinal
records of the number, time of day, and duration
of breastfeedings of infants between 2 and 26 weeks
of age, but no information was provided on the volume
of milk consumed at each breastfeeding by these infants.
Previously, interest has focused on the nutrient intake
of the infant, and the total consumption has been quoted
with no information provided on the volume of milk
consumed from each breast.13,14 Therefore, it was not
possible to assess how the infant feeds to appetite in relation
to the volume of milk available in the mother’s breasts.
Furthermore, the literature on the frequency of breastfeeding
generally fails to define what constitutes a breastfeeding.
Although Ho¨ rnell et al11 defined “one breastfeeding
episode” as the “duration of suckling 2 minutes
or longer and separated from previous breastfeed by
at least 30 minutes,” this does not consider whether
the infant fed from 1 breast or both during that episode. In
this article, we investigate the volume and the pattern
of milk intake in a cross-sectional study of 1- to 6-month-old
infants who were being exclusively breastfed on
demand, and we examine the contribution of each
breast. This is the first article to describe the variation in
the volume of milk consumed from each breast at
each breastfeeding, the degree of fullness of each breast
before and after each breastfeeding, and the fat content
of the milk consumed from each breast throughout the
day and night. This will provide a normal reference range
to enhance clinicians’ support for breastfeeding mothers. METHODS Data
were collected from 71 mothers who were exclusively breastfeeding
on demand healthy, term infants who
were aged between 1 and 6 months. These mothers were
participants in studies that were conducted in this laboratory
from 2000 to 2004.15–17 These studies were approved
by the Human Research Ethics Committee of The
University of Western Australia. The
mothers test-weighed their infants before and after
each breastfeeding from each breast on a Medela electronic
Baby Weigh Scale (Medela AG, Baar, Switzerland) for
a period of 24 hours plus 1 breastfeeding. A corrected
24-hour production for each breast then was determined
using these data, but no correction for infant insensible
water loss was made; therefore, milk production may
be underestimated by 3% to 10%.18–20 All measurements
of breastfeed amounts, storage capacity, and
milk production are expressed in grams that can be considered
to be nearly equivalent to mL because the density
of milk is 1.03 g mL_1.21
For each mother, the breast
that had the higher 24-hour production was termed
“more productive” and the breast that had the lower
24-hour production was termed “less productive.” In
addition, milk samples (_1
mL) were collected by hand
expression into 5-mL polypropylene plastic vials (Disposable
Products, Adelaide, Australia), immediately before
and after each breastfeeding from each breast. Samples
were frozen as soon as possible and kept at _15°C
for analysis. The cream content of the milk samples was
measured by the creamatocrit method,22 and the
fat content of each sample, in grams per liter, was calculated
as 5.37 _
creamatocrit
_
5.28.15 The
original estimation of fat content as a function of e388
KENT,
et al at
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of breast emptying was introduced by Daly et al,23 whereby
fat content was best predicted using a quadratic function
with degree of emptying as a predictor. Although time
since last breastfeeding and individual breast
had a small effect, the best predictor of fat content was
degree of emptying. This accounted for 68% of variation,
which was deemed satisfactory given the physiologic
process being measured. Degree of fullness was
calculated as 1 _
degree
of emptying, and it was obtained
via inverse calculation of degree of emptying using
the equation fat _
21.50
_
9.38
_
(degree
of emptying)
_
70.99
_
(degree
of emptying)2.23 This relationship between
degree of emptying and fat content was
individualized, whereby for each woman, minimal, median,
and maximal fat content over 24 hours was set to
correspond to degree of fullness of 1, 0.6892, and 0, respectively,
that protected against physiologically impossible estimates
(ie, degree of fullness exceeding 1 or becoming
negative). The storage capacity (the amount of milk
available to the infant when the breast is full) was determined
using a regression line relating change in degree
of fullness at each feeding to the amount of milk removed
from the breast at that feeding. Assuming that a
change in degree of fullness of 0 corresponds to a feeding
amount of 0, the regression line was forced to pass
through the origin. Storage capacity then could be calculated
as the amount of milk that corresponds to a change
in degree of fullness of 1. The volume of available milk
in the breast before each breastfeeding was calculated
as the degree of fullness multiplied by the storage
capacity of the breast. We
defined a breastfeeding as an infant’s taking milk from
1 breast. When the next breastfeeding was _30 minutes
after the end of the first, the breastfeeding was considered
to be unpaired. When the infant took milk from
the other breast within 30 minutes of finishing on the
first breast, the breastfeedings were considered to be paired.
When the infant fed again from the first breast within
30 minutes of finishing on the second breast, the breastfeedings
were considered to be clustered. A meal was
defined as an unpaired breastfeeding, or 2 paired breastfeedings,
or 3 clustered breastfeedings. This defi- nition
of a “meal” is equivalent to “1 breastfeeding episode” as
defined by Ho¨ rnell et al.11 Four breastfeedings were
0 g when the infant went to the breast and apparently suckled
but there was no difference between the infant’s
weight from before to after the breastfeeding. For
this study, the day was divided into 4 intervals. Morning
was considered to be from 4:01 AM to 10:00 AM, day
was 10:01 AM to 4:00 PM, evening was 4:01 PM to 10:00
PM, and night was 10:01 PM to 4:00 AM. Descriptive
summaries of continuous data used means
and SDs or medians and interquartile ranges (IQRs),
depending on data normality. Inference was based
on summary data averaged over 24 hours (n
_ 71),
overall summaries for individual breasts (n
_
142), and
all individual breastfeedings recorded over 24 hours (n
_
775).
Analyses of individual breastfeedings were weighted
according to the number of breastfeedings recorded per
woman. Paired and unpaired univariate comparisons of
summary data were performed using t
tests or
their nonparametric equivalents depending on data normality.
Multivariate analysis was based on analysis of variance
with repeated measures performed using Proc GLM
(SAS 8.02; SAS Institute Inc, Cary, NC), and goodness of
fit was assessed via analysis of residuals. Linear and
polynomial regression analyses were used to assess relationships.
Two-sided P
values
are quoted, and P
_ .05
was regarded as statistically significant. RESULTS The
characteristics of the mothers are presented in Table 1.
There were 41 male and 30 female infants. There was no
significant difference either between the mean age of the
male and female infants or in the age and parity of their
mothers. Frequency
and Volume of Breastfeedings A
total of 775 breastfeedings were monitored. Each infant had
11 _
3
breastfeedings per day (range: 6–18). The
interval between breastfeedings was 2 hours 18 minutes
_
43
minutes (range: 4 minutes to 10 hours 58 minutes).
Of these breastfeedings, 345 (44.5%) were unpaired
(182 from the more productive breast and 163 from
the less productive breast), with an interval of _1 hour
until the next breastfeeding for 90% of these breastfeedings.
A total of 412 (53.2%) breastfeedings were
paired, and 18 (2.3%) were clustered. That is, there were
7.9 _
1.8
meals per day (range: 4–13), and the interval
between meals was 3 hours 2 minutes _
41 TABLE
1 Subject
Characteristics Mean_SD
Range Mother Age,
y 31.8_4.3
23–42 Parity
1.7_0.8
1–4 Infant Age,
wk 15.3_5.9
4–26 24-h
breast milk intake, g Total
788_169
478–1356 More
productive breast 459_106
253–769 Less
productive breast 339_90
161–553 Breast
storage capacity, g More
productive breast 193_60
76–382 Less
productive breast 164_53
74–320 Average
breastfeed volume, g More
productive breast 84_28
32–131 Less
productive breast 67_26
27–147 Breastfeed
frequency, feeds per day More
productive breast 5.6_1.6
3–9 Less
productive breast 5.4_1.5
3–9 Fat
content of milk, g/L More
productive breast 41.3_8.4
22.5–60.8 Less
productive breast 40.9_8.4
22.3–61.6 PEDIATRICS
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(range: 40 minutes to 10 hours 58 minutes). Thirteen
percent of infants always had paired breastfeedings (n
_
9),
30% of infants always had unpaired breastfeedings (n
_
21),
and the remaining 57% of infants had a
mixture of paired and unpaired breastfeedings (n
_ 41). There
were no changes in the breastfeeding frequency with
age of the infant and no significant difference in
breastfeeding frequency between girls and boys. The
more productive breast was fed from as frequently as
the less productive breast, and when the breastfeedings were
paired, the more productive breast was offered first
as frequently as the less productive breast. There was
no relationship between the number of breastfeedings per
day and the 24-hour milk production of the mothers. The
infants took 76.0 _
12.6
g (range: 0–240 g) at each
breastfeeding. There was an inverse relationship between
the number of breastfeedings per day and the average
breastfeeding volume (r2
_
0.442;
P
_
.001;
n
_ 142
breasts). The average meal was 101.4 _
15.6
g (range:
0–350 g). The average breastfeeding volume was unrelated
to the age of the infant (P
_
.421),
but there was
an increase in the maximum breastfeeding volume with
advancing age between 4 and 26 weeks (r2
_
0.09; P
_
.010).
The maximum breastfeeding volume of boys was
greater than that of girls (154.6 _
54.8
g for boys vs 129.8
_
29.0
g for girls; P
_
.029),
but there was no significant
difference in the average breastfeeding (79.3 _
26.9
g for boys vs 73.0 _
22.4
g for girls; P
_
.299). The
average breastfeeding from the more productive breast
was higher than that from the less productive breast
(P
_
.001;
Table 1), and individual breastfeedings from
the more productive breast were larger than from the
less productive breast (P
_
.001;
Fig 1). Breastfeeding
volumes were significantly associated with
breastfeedings’ being unpaired, paired, or clustered. For
an unpaired breastfeeding, the infants consumed 90 _
26
g (range: 0–240 g). When the breastfeedings were paired,
the infants consumed 73 _
11
g (range: 5–185 g) for
the first breast and 54 _
9
g (range: 0–176 g) from the
second. For the clustered breastfeedings, the infant took
a median of 42 g (IQR: 31–103 g) from the first breast,
a median of 20 g (IQR: 8–44 g) from the second breast,
and a median of 31 g (IQR: 6–73 g) from the third breast.
For the paired breastfeedings, when the more productive
breast was fed from first, the infant took more
(P
_
.0001)
from the first breast than from the second
breast (Fig 1). When the less productive breast was
fed from first, the infant took similar volumes from each
breast (Fig 1). Storage
Capacity, Degree of Fullness, and Available Milk The
storage capacity of each breast was 179 _
59
g (range:
74–382 g). There was no association between the
storage capacity and time after birth (r2
_
0.015;
P
_ .155;
n
_
142
breasts). There was a positive relationship between
the storage capacity and the 24-hour milk production (r2
_
0.393;
P
_
.001;
n
_
142
breasts), the maximum
breastfeeding (r2
_
0.460;
P
_
.001;
n
_
142 breasts),
and the average breastfeeding (r2
_
0.297;
P
_ .001;
n
_
142
breasts) from each breast. There was a significant
difference (P
_
.013)
between the total breast storage
capacity for mothers who were breastfeeding boys
(394 _
126
g) compared with those who were breastfeeding
girls (333 _
71
g). There was a significant difference
(P
_
.003;
Table 1) between the storage capacity of
the more productive breast (193 _
60
g; range: 76–382
g) and the less productive breast (164 _
53
g; range:
74–320 g). For
unpaired breastfeedings, there was no significant difference
between the more and less productive breasts in
the degree of fullness of the breast at the beginning of the
feed (prefeed; 0.69 _
0.10).
This was significantly higher
(P
_
.032)
than the prefeed degree of fullness of the
first breast of a paired breastfeeding. For paired breastfeedings,
there was a significant difference (P
_ .001)
between the prefeed degree of fullness for the breasts
(0.63 _
0.08
and 0.52 _
0.07
for the first and second
breasts, respectively) regardless of whether the breast
was the more or less productive. When the breastfeedings were
clustered, the “third” breast had a prefeed degree
of fullness of 0.26 _
0.07.
For the 0-g feeds, the mean
difference in the cream content of the samples that were
collected before and after the breastfeeding was 1.4%,
and the prefeed degree of fullness ranged from 0.21
to 0.58. There was a significant relationship between the
volume of milk available in the breast and the volume
of milk consumed at each breastfeeding (r2
_ 0.358;
P
_
.001;
n
_
775
breastfeedings). For
unpaired breastfeedings, the available milk was different
between the more productive breast and the less
productive breast (P
_
.003;
Fig 2), but a similar percentage
of the available milk was removed (72 _
7% FIGURE
1 Volume
of milk consumed at a breastfeeding from the more productive breast (e)
and the
less productive breast (u)
when the breastfeedings were unpaired or paired. Values are
means with SEM represented by vertical bars. a More productive and less
productive breasts
are different (P_.0001). e390
KENT,
et al at
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69 _
8%
from the more and less productive breasts, respectively).
The degree of fullness of the breast at the end
of the breastfeeding (postfeed) was 0.19 _
0.06
for both
the more and the less productive breasts. When
the breastfeedings were paired and the more productive
breast was fed from first, there was a significant difference
in the available milk (118 _
19
g and 80 _
14
g for the more and less productive breasts, respectively; P
_
.0001;
Fig 2), whereas when the less productive breast
was fed from first, there was no significant difference
between the breasts in the available milk (Fig 2).
The percentage of available milk that was removed during
paired breastfeedings was significantly less than during
an unpaired breastfeeding (P
_
.0001),
but a similar
percentage of the available milk was removed (63 _
8%),
regardless of the order from which the breasts were
fed. There was a significant difference (P
_
.003) between
the postfeeding degree of fullness for the breasts
(0.20 _
0.05
and 0.26 _
0.05
for the first and second
breasts, respectively) regardless of whether the more
or less productive breast was first. For the clustered breastfeedings,
47 _
13
g was available in the “third” breast,
47% of the available milk was removed, and the postfeeding
degree of fullness was 0.19 _
0.05
(n
_
4). Total
24-Hour Milk Production The
overall 24-hour milk production for both breasts combined
was 788 _
169
g (range: 478–1356 g; Table 1).
A significant difference in the 24-hour milk production between
the more productive and less productive breasts
was evident (P
_
.001;
Table 1), with an absolute median
difference between the breasts of 106 g (IQR: 39–173
g; range: 5–441 g). For the majority of the mothers
(76%), the right breast was the more productive, resulting
in a significant difference between the right
and the left breasts (426 _
116
g [range: 161–769 g]
and 372 _
109
g [range: 177–601 g], respectively; P
_ .003). There
was a significant difference in milk production (P
_
.036)
between mothers of boys (831 _
187
g) and those
of girls (755 _
151
g). No significant effects on milk
production were associated with time after birth (r2 _
0.037,
n
_
71),
parity (r2
_
0.051,
n
_
71),
or maternal
age (r2
_
0.028,
n
_
71).
There was no relationship between
the “cold” and “warm” months of the year
and the 24-hour milk production (r2
_
0.010;
P
_ .413). Overall,
infants consumed 64% of their 24-hour intake (497
_
17
g) in 6.8 _
0.3
feedings between 6 AM and
6 PM and 275 _
13
g in 4.0 _
0.2
feedings between 6
PM and 6 AM. Between 2 PM and 2 AM, they consumed 322
_
12
g (42% of their 24-hour intake) in 5.1 _
0.2 feedings
and 450 _
16
g in 5.7 _
0.2
feedings between 2
AM and 2 PM. Younger infants, up to 9 weeks of age, consumed
443 _
32
g (61% of their 24-h intake) in 7.0 _
0.7
feedings between 6 AM and 6 PM and 275 _
15
g in 4.7
_
0.4
feedings between 6 PM and 6 AM. Between 2 PM and
2 AM, they consumed 328 _
15
g (45% of their 24-hour
intake) in 5.8 _
0.6
feedings and 390 _
29
g in 5.6
_
0.7
feedings between 2 AM and 2 PM. Night
Feedings The
majority (64%) of infants breastfed between 1 and 3 times
at night (10 PM to 4 AM), and the number of nighttime
breastfeedings did not change between 4 and 26
weeks. Only 36% of infants did not feed during the night. There
was no significant difference in the total 24- hour
milk production for infants who did and did not breastfeed
at night. Mothers of infants who breastfed at night
had a total breast storage capacity of 342 _
95
g, which
was not significantly different (P
_
.078)
from that
of mothers of infants who did not breastfeed at night
(386 _
108
g). There was no significant difference in
the total number of breastfeedings per 24 hours between infants
who did and did not breastfeed at night, with
the median numbers of 11 breastfeedings (IQR: 8–13;
range: 6–18) and 10 breastfeedings (IQR: 10–12; range:
6–17), respectively (P
_
.890).
Infants who breastfed
at night had fewer breastfeedings at night (median: 1;
IQR: 1–2) than during any other interval (P
_ .001).
There was a median of 3 breastfeedings (IQR: 3–4; range:
1–6) during all other intervals, irrespective of whether
the infants breastfed at night. Statistically
different volumes were measured at different intervals
of the day (P
_
.019;
Fig 3), with the night
breastfeedings being the largest and increasing with
both age and degree of fullness of the breast (r2
_ 0.255;
P
_
.001;
n
_
81).
Infants who breastfed at night had
significantly larger breastfeedings during the night compared
with the morning (P
_
.012),
the day (P
_ .002),
and the evening (r2
_
0.294;
P
_
.001;
n
_
496 FIGURE
2 Volume
of milk available before each breastfeeding from the more productive (e)
and the
less productive (u)
breasts when the breastfeedings were unpaired or paired. Values are
means with SEM represented by vertical bars. More productive and less
productive breasts
are different (a P_.003;
b P_.0001). PEDIATRICS
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Fig 3A). From the less productive breast, the
infants had smaller breastfeedings in the evening than
during the night and the morning (P
_
.05).
Although the
night breastfeedings were larger from the more
productive breast, because the night breastfeedings were
less frequent than during the rest of the day, 20 _ 7%
of the total 24-hour milk production was consumed at
night, which was significantly less (P
_
.008)
than that
taken during the morning (28 _
9%),
the afternoon (28
_
8%),
and the evening (24 _
8%). Infants
who did not breastfeed at night had signifi- cantly
larger breastfeedings during the morning than during
the day and the evening (P
_
.001)
from both the more
and the less productive breasts (Fig 3B). These infants
took more of the 24-hour milk production (40 _ 12%)
during the morning than during the day (29 _ 10%)
and during the evening (25 _
9%;
P
_
.001). The
volume of milk that was available at the beginning of
a breastfeeding in the breasts of mothers who breastfed
at night ranged from 88.9 g for the less productive breast
in the evening to 125.8 g for the more productive
breast at night. For mothers who breastfed only
during the day, the volume of milk that was available at
the beginning of a breastfeeding ranged from 83.7
g in the evening for the less productive breast to 156.0
g in the morning for the more productive breast. For
mothers who breastfed at night, more milk remained in
the breast at the end of breastfeedings in the morning
and the night (degree of fullness: 0.27 and 0.24, respectively)
than during the day or the evening (degree of
fullness: 0.17 and 0.18, respectively; P
_
.001).
For mothers
who breastfed only during the day, more milk remained
in the breast at the end of breastfeedings in the morning
(degree of fullness: 0.31) than during the day or
the evening (degree of fullness: 0.18 and 0.20, respectively; P
_
.001). Fat
Content of Breast Milk The
average fat content of the milk was 41.1 _
7.8
g/L and
ranged from 22.3 to 61.6 g/L. The average fat content was
not associated with either the time after birth (r2
_
0.036,
n
_
71)
or the number of breastfeedings during
the day (r2
_
0.013,
n
_
775).
There was an inverse
relationship between the mean fat content of the milk
and the 24-hour milk intake from that breast (P
_ .007,
r2
_
0.089,
n
_
142).
The average 24-hour fat intake
of the infants was 32.0 _
7.7
g (range: 15.4–49.5 g)
and was not related to the frequency of breastfeedings. Analysis
of the individual breastfeedings showed that there
was no effect on the average milk fat content as a result
of the gender of the infant (P
_
.160);
more or less productive
breast (P
_
.332);
unpaired, paired, or clustered breastfeedings
(P
_
.339);
or whether the infant breastfed
at night or not (P
_
.830).
The mean fat content
of the milk was significantly related to time of day
(P
_
.001)
and was higher (P
_
.008)
during the day and
the evening (42.8 _
9.1
and 43.2 _
9.1
g/L, respectively) compared
with the morning and the night (37.1 _
10.1
and 37.2 _
10.3
g/L, respectively). The
interval between meals was independent of the volume
of the previous meal (paired or unpaired breastfeeding). The
interval was also independent of the average fat
content of the milk consumed in that meal or the amount
of fat in the meal. DISCUSSION Frequency
and Volume of Breastfeedings The
spectrum of breastfeeding behavior of normal infants who
were exclusively breastfed ranged between having
a few large breastfeedings and having frequent small
breastfeedings during 24-hour periods, and the infants
distributed the number of breastfeedings evenly when
comparing morning with afternoon and evening, with
fewer breastfeedings at night. The wide range in FIGURE
3 Volume
of milk consumed at a breastfeeding from the more productive breast (e)
and the
less productive breast (u)
during the morning (4:01 AM to 10:00 AM), day (10:01 AM to 4:00
PM), evening (4:01 PM to 10:00 PM), and night (10:01 PM to 4:00 AM) by
infants who breastfed
at night (A) or did not breastfeed at night (B). Values are means with SEM represented
by vertical bars. More productive and less productive breasts are
different (a
P_.05;
b P_.0001). e392
KENT,
et al at
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of “meals” that we observed was very similar to
that described by Butte et al,24 Cregan et al,10 and Ho¨
rnell et al.11 The inverse relationship between the number
of breastfeedings per day and the average breastfeeding
volume is consistent with the lack of a relationship
between the number of breastfeedings per day
and the 24-hour milk production of the mothers. The
volume of milk consumed during a breastfeeding depended
on (1) whether the breast was the more or less productive
breast, (2) whether the breastfeeding was unpaired
or paired, (3) whether it was the first or the second
breast of paired breastfeedings, and (4) the time of
day (Figs 1 and 3). For
53% of the meals, 1 breast was sufficient to satisfy the
infant for at least 1 hour. This is consistent with the unpaired
breastfeedings, particularly from the more productive breast,
being larger than the average breastfeeding (Fig
1) and supports the advice of Riordan and Aurbach25(p247)
that after breastfeeding becomes established, it
may not be necessary to use both breasts at each
meal, and also the recommendation of the National Health
and Medical Research Council6 that both breasts be
offered at each meal, but the infant may or may not feed
from the second breast. For the 44% of the breastfeedings that
were paired, if the second breast was the less
productive breast, then the breastfeeding volume could
be considered to be a “top up.” However, if the second
breast was the more productive breast, then the infant
took an equal volume to the first breast. Therefore, the
milk yield from the second breast, when the infant
chooses to feed from it, may provide a significant volume
of milk. The
larger breastfeedings in the morning compared with
the evening were also observed by Butte et al.24 For infants
who breastfed at night, although there were fewer
breastfeedings during this time, those from the more
productive breast were the largest of the 24-hour period,
and the nighttime intake composed 20% of the total
24-hour intake. For the infants who did not breastfeed at
night, the morning breastfeedings were the largest (Fig
3B). Some
mothers are concerned about the frequency of breastfeeding
and wish to extend the interval between breastfeedings.
We found that some infants would breastfeed
again within 1 hour after breastfeedings of up to
175 g, and others would not breastfeed for _8
hours after
a breastfeeding of as little as 35 g. In fact, the interval
after the largest meal of 350 g was only 3 hours 35
minutes. Infants of the 5 mothers with total storage capacity
of _235
mL all breastfed at night. However, most
of the infants of mothers with larger storage capacities chose
to breastfeed at night. Infants may need to feed
at night if they have a relatively small stomach capacity
and/or a rapid gastric emptying time. Storage
Capacity, Degree of Fullness, and Available Milk The
storage capacity that was calculated in this study is similar
to that calculated by Kent et al26 for the first 6 months
of lactation (196 _
57
g). It is smaller than that measured
by Daly et al27 (242 mL; SD: 129) by Computerized Breast
Measurement; however, that study included 1
breast with an unusually large storage capacity of
606 mL. The relationship between storage capacity of the
breast and the 24-hour milk production is similar to that
found by Kent et al.26 In the current cross-sectional study,
there was no relationship between the storage capacity
of the breast and the age of the infant. However, in
a longitudinal study, the mean storage capacity at 1 month
(179.9 _
20.2
g) increased to 234.6 _
17.5
g at 6 months
(mean _
SEM),
indicating that the storage capacity of
the breast can change during lactation.26 Because the
maximum breastfeeding increased between 4 and
26 weeks and there was a relationship between the storage
capacity and the maximum breastfeeding, it is likely
that the storage capacity of the breast is able to change
to meet an increase in demand for milk. Anecdotally,
mothers usually first offer the breast that feels
more full. The data on the prefeeding degree of fullness
of the breast confirm this subjective choice of the
mothers. The prefeeding degree of fullness and the storage
capacity allow calculation of the volume of available milk
in the breast. The volume of milk that is available
accounted for most of the differences in volume of
milk consumed at each breastfeeding (Figs 1 and 2).
For unpaired breastfeedings, not only was there more milk
available in the more productive breast, but also the infants
took a higher percentage of that available milk than
during a paired breastfeeding. The
observation that the breasts are rarely drained at the
end of a breastfeeding was also noted by Dewey et al,20
who found that an extra 12% of milk could be expressed
after a breastfeeding. Because breast expression is
not always effective in removing all of the available milk,15
this finding is consistent with the infants’ removing
63% to 72% of the available milk during a breastfeeding.
This suggests that the breasts do not need to
be drained at every feeding to maintain adequate milk production. Total
24-Hour Milk Production The
24-hour milk production was within the normal range
of 440 to 1220 g,26 except for 2 mothers, who produced
1298 g and 1356 g. The average of 798 g is similar
to the data presented by Dewey and Lo¨ nnerdal.14 It
is important to note the wide SD and bear in mind that the
variation in milk production is related to the variation in
the growth rates of the infants.12,26,28 In addition, the
higher milk intake of male infants was also noted by Butte
et al29 and is consistent with their higher growth rate.30
The lack of effect of either maternal age or parity PEDIATRICS
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milk production is in agreement with the findings of Dewey
and Lo¨ nnerdal.14 Consistent
milk intake from 1 to 6 months supports previous
findings.26 This is not surprising considering 2 factors.
First, younger infants (1–3 months of age) grow more
rapidly than older infants (4–6 months of age).30 Second,
smaller infants have a larger surface area to volume
ratio and therefore have a relatively higher metabolic rate
per kilogram of body weight31 and use relatively more
of their nutrient intake for maintenance of body
temperature than do older, heavier infants. Differences
in milk production of right and left breasts have
been noted previously. Mitoulas et al32 found a significant
difference between breasts, with the right breast
being more productive (443 vs 356 g/24 hours). In
addition, Cox et al33 showed that the right breast was often
more productive than the left. In this context, it is interesting
to note that when we measured the milk production
of 4 mothers who were exclusively expressing their
milk for their infants (_660
g/day), there was a
significant difference (P
_
.03)
between the left and the
right breasts (unpublished results). Three of these mothers,
who were double pumping and therefore submitting both
of their breasts to equivalent vacuums and times
of expression, had the largest differences between the
breasts. This leads us to suggest that the difference in milk
production between the breasts may be attributable to
differences in intrinsic milk production rather than the
infant’s preference. The 24-hour milk production of mothers
of infants who breastfed at night was the same as
for those who did not breastfeed at night, similar to the
observations of Butte et al.24 The
current data for infants up to 26 weeks of age confirm
the findings of Matheny and Picciano8 for 4-week-old
infants that more milk is consumed between 6
AM and 6 PM and less is consumed between 2 PM and 2 AM.
The uneven distribution of the volumes of breastfeedings of
both infants who breastfeed at night and those
who do not breastfeed at night (Fig 3) explains why
doubling of either of these 12-hour intakes will result
in significant inaccuracies in estimation of 24- hour
milk consumption. Therefore, our measurements confirm
that in our society, a full 24-hour period of measurement
of milk intake is necessary for accuracy. Fat
Content of Breast Milk The
fat content of the milk that we measured was similar to
that measured by Dewey and Lo¨ nnerdal,14 and the 24-hour
fat intake of the infants was similar to that measured
previously.12,14 Fat content of the milk at different times
of day reflects the higher degree of milk removal
during the day and evening and the higher degree
of fullness in the morning and night. The changes in
fat content of milk from the beginning to the end of the
first and second breasts of a paired breastfeeding described
by Woodward et al34 can be explained by the degrees
of fullness that we have calculated. The lower fat content
of milk from the first breast at the beginning of the
breastfeeding that they measured reflects the mother’s starting
to feed her infant on the fuller breast, and the
higher fat content of milk from the first breast at the end
of the breastfeeding reflects the higher degree of milk
removal from the first breast. Because
the breast was not full at the beginning of each
breastfeeding for the whole day, the fat content of the
fore-milk was not always low. Because the fat intake of
the infants was not related to the frequency of breastfeedings, mothers
can be reassured that infants who take frequent
small breastfeedings have the same daily fat intake
as infants who take infrequent large breastfeedings. An
understanding of the patterns of milk intake by the
breastfed infant has implications for mothers who need
to express their milk either fully for a preterm infant
or when they return to the paid workforce. Given the
variability in breastfeeding patterns, it may be unreasonable to
expect all breasts to yield the same volume of
milk at the same rate when the mother is using an electric
breast pump, and the breast may not need to be totally
drained at every expression to maintain an adequate supply
of milk. Breast pump settings and regimens may
need to be customized for each mother. CONCLUSIONS Healthy,
exclusively breastfed 1- to 6-month-old infants consume
0 to 240 g of milk between 6 and 18 times during
24 hours, with 64% of infants breastfeeding 1 to 3
times at night. The right breast usually produces significantly more
milk than the left, and the volume of milk
consumed at each breastfeeding is related to the volume
of milk available in the breast, whether the breastfeeding
is unpaired or paired, and the time of day. On
average, 67% of the available milk is consumed at each
breastfeeding. The fat content of breast milk varies between
mothers (22.3–61.6 g/L) and within and between breastfeedings,
but the amount of fat consumed by
the infant is independent of the frequency of breastfeeding. ACKNOWLEDGMENTS The
research described in this article was funded by Medela
AG, which is gratefully acknowledged. We
thank the participating breastfeeding mothers and infants
for their time, the Australian Breastfeeding Association for
recruiting volunteers, and Tracey Williams for
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10.1542/peds.2005-1417 2006;117;387-395
Pediatrics Doherty
and Peter E. Hartmann Jacqueline
C. Kent, Leon R. Mitoulas, Mark D. Cregan, Donna T. Ramsay, Dorota A. Throughout
the Day Volume
and Frequency of Breastfeedings and Fat Content of Breast Milk This
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