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R E S E A R C H Open Access
Association between breastfeeding and
new mothers’sleep: a unique Australian
time use study
Julie P. Smith
1*
and Robert I. Forrester
2
Abstract
Background: Infant sleep is of great interest to new parents. There is ongoing debate about whether infants fed
with breastmilk substitutes sleep longer than those exclusively or partially breastfed, but what does this mean for
the mother? What expectations are realistic for mothers desiring to exclusively breastfeed as recommended by
health authorities?
There are both biological and social influences on infant and maternal sleep. More accurate information on average
maternal sleep hours for diverse feeding practices may help guide realistic expectations and better outcomes for
mothers, infants and families.
Methods: Using a unique time use dataset purposefully designed to study the time use of new mothers, this study
investigated whether the weekly duration of maternal sleep, sleep disturbance, unpaid housework, and free time
activities differed by detailed feeding method. The study collected 24/7 time use data from 156 mothers of infants
aged 3, 6 and/or 9 months between April 2005 and April 2006, recruited via mother’s groups, infant health clinics,
and childcare services throughout Australia. Sociodemographic and feeding status data were collected by
questionnaire. Statistical analysis used linear mixed modelling and residual maximum likelihood analysis to compare
effects of different infant feeding practices on maternal time use.
Results: There were no significant differences in time spent asleep between lactating and non lactating mothers,
though lactating mothers had more time awake at night. Lactating mothers spent more time (8.5 h weekly) in
childcaring activity (p= 0.007), and in employment (2.7 vs. 1.2 h, p< 0.01), but there were no significant differences
in free time. Those not breastfeeding spent more time in unpaid domestic work.
Exclusive breastfeeding was associated with reduced maternal sleep hours (average 7.08 h daily). Again, free time
did not differ significantly between feeding groups. Exclusively breastfeeding mothers experienced reduced sleep
hours, but maintained comparable leisure time to other mothers by allocating their time differently. Domestic work
hours differed, interacting in complex ways with infant age and feeding practice.
Conclusions: Optimal breastfeeding may require realistic maternal sleep expectations and equitable sharing of paid
and unpaid work burdens with other household members in the months after the birth of an infant.
Keywords: Maternal time use, Sleep, Work, Breastfeeding, Lactation, Breastmilk
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* Correspondence: julie.smith@anu.edu.au
1
Research School of Population Health, College of Health and Medicine, The
Australian National University, Canberra, Australia
Full list of author information is available at the end of the article
Smith and Forrester International Breastfeeding Journal (2021) 16:7
https://doi.org/10.1186/s13006-020-00347-z
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Background
Sleep hours of infants are an issue of great interest
among new parents, and are investigated in many clin-
ical sleep studies [1]. There is also ongoing debate about
whether infants fed with breastmilk substitutes sleep
longer than those exclusively or partially breastfed [2–6],
but what does this mean for the mother? What expecta-
tions are realistic for mothers desiring to exclusively
breastfeed as recommended by health authorities? Con-
cerns about infant sleep arise from possible associations
with later developmental or health problems, but also
arise due to links with maternal anxiety or postnatal
depression.
Research in this area is hindered by lack of suitable
time use and infant feeding data, and by the complex
interrelationship between maternal and child sleep. Nu-
merous studies examine infant sleep, and some consider
infant feeding, but most studies in this area focus on in-
fant, not maternal, sleep hours. Most also fail to consider
how mothers’sleep and other free time might adapt to
demands of ‘night-time parenting’within the context of
their other daily activities.
A better understanding of infant sleep patterns can
benefit parents by informing them of what sleep patterns
may emerge in their newborn and when more mature
sleep development may be expected, and may also help
health professional and childcare advisors in counselling
parents and guiding realistic parental expectations. This is
especially important in the light of growing evidence that
interventions to promote infant sleep can have unintended
adverse consequences including increased maternal anx-
iety or premature weaning from breastfeeding [7].
Breastfeeding is well established as an important
underpinning of lifelong maternal and child health, as
well as supporting child development. Breastfeeding ex-
clusively for six months with continued breastfeeding to
2 years and beyond is recommended by health author-
ities, for promoting both child and maternal health and
wellbeing [8–19].
What should mothers who intend to exclusively
breastfeed realistically expect about sleep, for them-
selves, and for their infant at various ages, and what
strategies help families accommodate and adjust to
night-time parenting needs of infants?
There are both biological and social influences on in-
fant and maternal sleep, and the existing research in this
area is diverse in methodologies and findings [1], as dis-
cussed in more detail below. Mothers’sleep expectations
may conform to prevailing social norms for adult sleep,
which can be unrealistic for caregivers of newborns.
Maintaining exclusive breastfeeding could require
mothers to allocate their time differently to mothers
who introduce breastmilk substitutes or complementary
foods before 6 months, for example, feeding frequently
and during the night in order to build an adequate milk
supply. More accurate information on average maternal
sleep hours for diverse feeding practices may help guide
realistic expectations and better outcomes for mothers,
infants and families.
Infant sleep and suckling
Maternal sleep can be anticipated to be highly influ-
enced by their infants’sleep. Numerous researchers have
examined infant sleep, including measuring how many
hours children sleep at different ages. A recent system-
atic review indicates that average 24-h sleep duration
among 3 month old infants is 12–18 h, changing only
slightly with age to 12.1–14.2 h at 6 months, and 11.3–
13.9 h at 9 months [1]. Average infant sleep duration is
influenced by cultural and social factors [20]. Some stud-
ies also suggest infant sleep hours are affected by feeding
method [2–6], (although very few studies compare ex-
clusively breastfed infants, and those partially or fully fed
with breastmilk substitutes including solid food). Vari-
ation of sleep hours by feeding method is consistent with
biological as well as social explanations. Components of
breastmilk may influence sleep patterns of infants [1,
21], and feeding rhythms also interact in complex ways
with development of more mature diurnal sleep rhythms
in newborns [22]. For example breastmilk contains hor-
mones such as leptin and melatonin influencing appetite
and sleep respectively, and milk fat content is lower dur-
ing the night and morning feedings [23]. It has been pro-
posed that diurnal sleep rhythms of infants consolidate
earlier than feeding rhythms [22].
Maternal sleep
Much of the literature on the topic of infant feeding and
sleep focusses on sleep of newborn infants. The extent
of actual or perceived disturbance of the mothers’daily
activities, such as disruption of maternal sleep, or time
available for necessary personal care, leisure or work ac-
tivities is investigated in fewer studies. Such investiga-
tions have tended to focus on implications of reported
infant sleep problems for maternal post-natal depression
risk [24].
Just as lactation biology influences infant sleep, mater-
nal sleep can also be expected to vary by feeding
method. In a US study, exclusively breastfeeding women
averaged 30 min more nocturnal sleep than women who
used formula at night, but measures of sleep fragmenta-
tion did not differ [25]. Lactation hormones such as pro-
lactin help mothers adapt to the stresses of caring for an
infant, including broken sleep [13,26,27]. Lactation
hormones also influence maternal nurturing behavior
and desire for proximity to the infant, in animals as well
as humans. For example, time use research on new
mothers in Australia suggests differences in the amount
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of time they spent holding and soothing breastfed com-
pared to non-breastfed infants and this was related to
the degree of breastfeeding [28,29].
Cultural and social factors
Time use is related in socially as well as biologically
complex ways to infant feeding. How sleep is perceived
rather than the objective duration of sleep may better in-
dicate its effect on maternal well-being [30,31]. Hence,
understanding of how the sleep hours of mother-infant
dyads relate to infant feeding needs to be placed within
the broader context of how mothers of newborns may
prefer or choose to allocate their time between sleep,
work (paid or unpaid) and leisure.
Time is increasingly recognised to be a resource
needed for good health [32], including for nurturing care
and breastfeeding of infants [28,33]. Who has access to
(spare) time resources has been shown in a recent study
to be significantly shaped by both socioeconomic class
and gender [32]. Being pressed for time (‘rushed’)is
linked to being a woman, a sole parent, or disabled, and
is also associated with lack of job control and work fam-
ily conflicts [32]. Thus, access to maternal sleep may de-
pend in part on cultural and social determinants of
monetary and time resources available to the mother for
infant care. Medical anthropology and ethnographic
studies suggest that maternal care activities such as
breastfeeding and introduction of other nutrition are
adaptive to resource pressures on mothers and their
families [34–36]. Time available for optimal infant care
including exclusive breastfeeding –which is time inten-
sive [33] - may depend on whether mothers need to con-
serve maternal resources. For example, undernourished
or time-pressed mothers may end exclusive breastfeed-
ing so they can allocate their time to securing food or
other essential resources.
A resource-economising perspective points to a previ-
ously unexamined mechanism by which mothers adapt
to nighttime parenting of infants. This is to reallocate
time, whether from daytime leisure or work commit-
ments, such as employment, childcaring or domestic
work, to sleeping or napping. Some mothers will have
more capacity to do this and maintain their preferred
amount of free time activities, or address needs for sleep
or personal care time, if they are resourced by others, in-
cluding other family members, extended kinship groups
or the wider community [37,38]. This can take the form
of help from others in dealing with domestic commit-
ments such as housework, shopping, or childcare. Alter-
natively, it might mean lower maternal hours in income
earning activities, such as that afforded by maternity
leave. As well as lactation biology affecting infant and
maternal sleep behaviours, research has shown cultural
differences in infant sleep [20].
The above suggests a significant role for cultural, so-
cial and economic factors in influencing infant and ma-
ternal sleep and its relation to infant feeding practices.
The extent to which caring for an infant interferes with
maternal activities such as free time for recreation and
socialising, and on work commitments, paid and unpaid,
is largely undocumented, but is a measure that may pro-
vide new understanding of how sleep duration of the
mother-infant dyad affects the health and well-being of
both. Sociological studies highlight the gendered nature
of sleep disruption among parents of young children
[39]. Recent studies show that an important outcome as-
sociated with improved access to maternity leave in
European countries is better maternal mental health [40,
41].
A novel way to explore the complexities and dynamics
of how mothers adapt to the bio-behavioral demands of
infant care and to their social context is by investigating
whether maternal time spent in key categories of daily
activities differs by detailed infant feeding practice.
Hence, this study asks how maternal sleep duration re-
lates to infant feeding practices and breastfeeding, and
explores how this fits into the broader context of
mothers’daily hours of work and leisure.
Methods
Aim
The aim of this study is to identify associations between
maternal sleep hours and feeding practices, and explore
how maternal sleep hours may relate to mothers’domes-
tic or other work commitments, and free time for leisure
or personal care.
Design, setting, and participants
Comprehensive time use data on maternal time in the
care of infants is rarely collected, particularly in official
time use surveys. The Time Use Survey of New Mothers
(TUSNM) was a unique nationwide Australian study
conducted through the Australian National University
(ANU) between April 2005 and April 2006 and specific-
ally designed to address deficiencies in existing time use
data collections. All participants gave written informed
consent before enrolment (Protocol 2005/51 approved
on 10 March 2005 by the ANU Human Research Ethics
Committee under the National Statement on Ethical
Conduct in Research Involving Humans (1999)) [42].
The survey purpose was described to participants as
‘measuring the time it takes to care for a baby’. Recruit-
ment was through national playgroup and breastfeeding
support organizations, maternal and child health profes-
sional networks, infant health clinics, and childcare cen-
ters. Mothers with infants up to age nine months were
eligible to participate in the survey and could participate
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in tracking sessions at time points when the target infant
age was three, six and/or nine months.
Data collection
Data on infant feeding method for the youngest child
(the ‘target infant’) during seven days of time use track-
ing was collected by questionnaire filled out by partici-
pant mothers. We excluded participants who recorded
time use for less than one 24-h day. Feeding method
over the 7 days of tracking was self-reported by partici-
pants in the following categories: (A) exclusive breast-
feeding; (B) exclusive formula feeding; (C) mixed
breastmilk and formula milk –no solids; (D) breastmilk
and solids; (E) formula milk and solids; (F) mixed breast-
milk and formula milk with solids. Self-report of feeding
method was verified by cross checking against individual
time use data on feeding activities. Mothers using breast
pumps were instructed to record expressing breastmilk
as ‘preparing feeds’; these few mothers were categorized
as breastfeeding mothers even though feeding this milk
might be by someone other than the mother.
Data collected from the mother by questionnaire also
included the number of hours and minutes another fam-
ily member (usually her partner or husband) was caring
for, and feeding the infant, and how many hours the in-
fant spent in paid childcare. Fathers were not invited to
participate in time use tracking mainly because of ethical
concerns to limit response burdens on households.
Socio-demographic data were also collected via the writ-
ten questionnaire.
Participants were asked to track their time use for
seven days, 24 h a day, using TimeCorder™time tracking
devices. These were posted to the mothers along with
the questionnaire at each tracking time point, that is,
within two weeks of the relevant anniversary of the tar-
get infant’s birthdate. Participants could record at target
infant age three months, six months and/or nine
months. Data on the frequency, duration, and time of
day of each activity was recorded through participants
pressing one of 25 buttons on the device corresponding
to their current activity.
Measuring and categorizing feeding method and time use
An important factor of interest in this study was infant
feeding practice. This was measured using two different
categorizations. We compared those giving ‘no’breast-
feeding (exclusive formula feeding (feeding category B)
& formula milk and solids (E)) with those giving ‘any’
breastfeeding (exclusive breastfeeding (A), mixed breast
milk and formula milk –no solids (C), breastmilk and
solids (D), mixed breastmilk and formula milk with
solids (F)) that is, ‘lactating’mothers. Maternal hours in
the different categories of activities were also compared
for the 6 detailed feeding categories noted above (A to F).
TUSNM design and measurement of time use was
based on the Australian Time Use Survey (henceforth
‘TUS’), [43]. last conducted by the Australian Bureau of
Statistics (ABS) in 2006. The TUS measures main activ-
ities in the general population as comprising ‘personal
care’;‘employment’;‘education’;‘domestic activities’;
‘purchasing goods and services’;‘voluntary work and
care’;‘recreation fitness and leisure’;‘social and commu-
nity interactions’, and ‘childcare’.
Topologies of time
Most quantitative time use studies categorise the hours/
minutes spent according to whether the activity is
contracted (employment and related travel) or commit-
ted (caregiving, unpaid or domestic work) or necessary
(personal care, sleep and eating) activities [44,45].The
balance is considered discretionary or free time, such as
for recreation and leisure or social activities. Figure 1
summarises this topology of activity categories, for the
TUS and as adapted for this study of maternal time use.
Dependent variables and summary measures were cre-
ated and categorized to represent necessary time,
contracted or committed time, or ‘free time’for mothers
of infants aged 3–9 months in line with the topology in
Fig. 1.
Time use variables for necessary activities are those re-
lated to sleeping, eating and other personal care. Corre-
sponding directly to main activity categories in the TUS,
the TUSNM included measures of the amount of time
spent on “other personal care”(which relates to activities
such as bathing or showering). The TUSNM variable la-
belled ‘sleep’is defined as maternal time spent “sleeping
or napping”. In this study necessary time is taken to ex-
clude ‘family meals’, and only includes meals eaten alone
by an adult. This is because in families with infants and
young children, adults’time at family meals is more akin
to childcare, as children need assistance and supervision
with eating, rather than being mainly personal care.
Hence, time measured by the TUSNM variable for ‘fam-
ily meals’is classified as committed time.
The time use of a mother is closely interrelated with
commitment to meeting the care needs of her infant.
Night-time parenting activities illustrate the interrela-
tionship of necessary with committed time in this cir-
cumstance, and the interrelatedness of the time use
activities of the mother-infant dyad. Participants were
instructed to record periods of time involving interrup-
tions to maternal sleep (‘sleeplessness including awake
while feeding a baby during the night’)as“sleeplessness”.
In this dataset, “sleeplessness”is defined as the cumula-
tive time the mother recorded being awake during the
night tending to the infant, or otherwise being awake
during the night. The ‘sleeplessness’categorization was
intended to provide for night-time infant care activity
Smith and Forrester International Breastfeeding Journal (2021) 16:7 Page 4 of 13
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such as the mother dozing and/or the infant feeding to
sleep. Nevertheless, where there was ambiguity about
how to classify any such activities throughout the study,
mothers were instructed to allocate their time according
to how they viewed the main purpose of their activity at
that time. Hence, ‘sleeplessness’could exclude time actu-
ally feeding the infant, if the mother viewed “breastfeed-
ing”rather than “sleeping or napping”as the main
purpose of her activity at that time. Likewise, nappy
changing at night would be categorized under “bathing,
changing or dressing”the child, if the mother considered
that to be the main purpose of her activity at that time.
Such a category of activity is not included in the TUS
which is designed for measuring time us of the general
population of adults not the distinctive time use activ-
ities of mothers of infants. This term was included in the
TUSNM to reflect the unique, dyadic characteristics of
this population sub group and time use activities of new
parents.
“Sleeplessness”is categorized here as committed time,
being a form of childcare. It is comparable to adults’com-
mitments to unpaid domestic work, or care of children.
Childcare in TUSNM involves the physical or the emo-
tional care of an infant, including feeding as well as sooth-
ing, holding, or bathing a child, consistent with TUS.
Reflecting the multitasking nature of infant care, a
summary measure of nighttime parenting, combining
hours of sleeping or napping, plus periods of disturbed
sleep (‘sleeplessness’) was also defined for this study,
which overlaps necessary and committed time. This vari-
able indicates how conflict between using time for ne-
cessary maternal sleep activity was reconciled with
commitment to maternal care of the infant at night.
The ABS TUS also includes measures of discretionary
activity, such as recreation and leisure, or social and
community interactions. These are similarly measured in
TUSNM, as ‘recreation’and ‘social’activity time use. To
provide further context for analyses of maternal sleep,
we report analyses of data on maternal time spent in our
summary measure, ‘free time’.‘Free time’is constructed
as the sum of maternal time spent in “recreation”activ-
ity and time spent in “social”activity.
Statistical analysis
T-tests and chi-square tests were used to compare the
socio-demographic characteristics of the two infant feed-
ing groups. Characteristics of participants who provided
time tracking data records at one, two or three time points
(that is, at infant ages three, six, and/or nine months) were
also compared, using the same techniques.
Fig. 1 Time use measures and topologies
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We used a residual maximum likelihood (REML) ana-
lysis in GenStat [46] to perform a linear mixed effects
analysis of the relationship between infant feeding cat-
egory, and the specified maternal time use activities, for
participants observed at three time points. Data for time
use variables were transformed by taking the square root
prior to analysis, to stabilize the variance.
A repeated measures approach to statistical analysis
was appropriate because at least one but up to three suc-
cessive time use and sociodemographic data observa-
tions were provided by participants when the target
infant was aged 3, 6 and/or 9 months, and because the
numbers of observations in the cells of the two-way ta-
bles were highly variable. The intention of using the
REML method is to address the repeated measures and
unbalanced nature of the data. REML exploits all avail-
able observations for each participant at the three time
points, rather than omitting information from partici-
pants with missing data, and puts more weight on cells
with more observations in a multi-way table.
A REML mixed effect model was preferred over trad-
itional approaches such as repeated measures analysis of
variance (ANOVA) as the focus of the study was the ef-
fect of infant feeding practice on maternal time use.
Mixed effect modelling allowed us to estimate the separ-
ate (main) effects of feeding category and infant age,
whilst also exploring how the interaction of these two
(fixed) factors affected maternal time use.
REML analyses were conducted for the two factors of
interest described earlier; ‘detailed feeding category’(six
levels), and breastfeeding (including mixed) versus non-
breastfeeding (two levels). The fixed terms in the model
were “infant age”,“factor of interest”, and the interaction
between these. The interaction checks the two-way table
between “infant age”and “factor of interest”to see
whether there are significant differences between any
pair of means in the table that is not attributable to ei-
ther the main effects of the fixed terms “infant age”or
“factor of interest”. The random terms were “target in-
fant”/“infant age”(which expands to “target infant”and
“infant age”within “target infant”).
The significance of fixed effects (p< 0.05) was assessed
on the transformed data using Wald statistics and ap-
proximate F-statistics. This is appropriate for assessing the
significance of both the main effects and the interaction
term in the model for fixed effects specified above.
Results
Participants
Recruitment generated 185 participants, from an un-
known number of contacts. Of 185 mothers giving con-
sent, 162 participated in postnatal time use tracking, and
156 contributed time use and socio-demographic data
records. This generated 327 usable data records of
maternal time use activities over seven days and nights
as inputs to the modelling.
The number of data records/observations exceeds the
number of participants because most provided time use
tracking data at more than one time point. For example,
31 observations were contributed by mothers who only
tracked once, while a further 134 observations were from
those who tracked twice. Around half of the 327 obser-
vations (n= 162) were from those who tracked three
times, firstly at three months of infant age, then at six
months, then again at nine months.
Table 1summarizes the dataset presenting informa-
tion on the age of the target infants at the maternal time
use tracking time points, the feeding categories of the
target infants at that time point, and tracking categories,
describing the number of participants who tracked at
one, two or three points. These observations are for 156
individual infants who may be in different feeding
groups at different ages, for example, being exclusively
breastfed at 3 months, but contributing an observation
in the ‘breastfeeding with solids’feeding group when
time use is tracked at 6 or 9 months.
Comparison of socio-demographic characteristics for
those doing one, two and three time use trackings also
showed no statistically significant differences in age of
the target child, age of the 2nd youngest child, number
of children, mother’s age, mother’s education, or
mother’s employment status between mothers who pro-
vided data at one, two, or three time points.
The TUSNM sample population had similar characteris-
tics to the Australian population of mothers of infants on
most key socio-demographic variables, though participants
were more likely to be first-time mothers, and more highly
educated. TUSNM also contained a higher prevalence of
breastfeeding mothers than would be expected from popu-
lation based studies of breastfeeding in Australia, such as
the Longitudinal Study of Australian Children and the Aus-
tralian Infant Feeding Survey [47–49].
Maternal age, number of children, the proportion with
only one child, and the age of second youngest child
were not significantly different between the breastfeed-
ing and non-breastfeeding groups, nor were there signifi-
cant differences in maternal employment, education
levels, and family income.
Maternal time use –sleep and free time comparisons for
combined feeding groups
Table 2comprises two parts, a and b, and compares the
activities of non-breastfeeding/non-lactating mothers
(“no breastfeeding”) with breastfeeding/lactating mothers
(“any breastfeeding”), and infant ages 3, 6 and 9 months.
The table presents back-transformed means. (The pre-
dicted means together with back-transformed means are
in the Supplementary Tables).
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The first half of the (Table 2a) reports the ‘main effect’
of no breastfeeding with any breastfeeding, on the ma-
ternal activities analysed, using the REML method to ap-
propriately weight the data over the different aged target
infants. These numbers, in effect, show hours of maternal
activity by breastfeeding status, averaged over the whole
sample. The second part of the (Table 2b) shows the ‘main
effect’of infant age 3, 6 or 9 months, on maternal activ-
ities, for either breastfeeding status (“some”or “no”).
So for example, in Table 2a, the average weekly hours
of maternal sleep for a non-breastfeeding mother are
58.13 regardless of the age of the child.Testing using
the Wald statistics and approximate F statistics did not
reveal any statistically signficant interaction between in-
fant age and breastfeeding status.
Similarly, in Table 2b the average weekly hours of ma-
ternal sleep for a infant aged 6 months are 57.32 regard-
less of the breastfeeding status of the child.
Table 1 Summary of observations and data collection: detailed feeding group by age of target infant, and data collection category
Detailed feeding group Observations by age of target child (n) Observations
(%)
3 months 6 months 9 months
A Breastfed only 79 15 1 95 (29.1%)
B Formula only 4 0 1 5 (1.5%)
C Breastfed and formula fed 2 1 0 3 (0.9%)
D Breastfed and solids 1 101 83 185 (56.6%)
E Formula fed and solids 0 11 11 22 (6.7%)
F Breastfed and formula fed and solids 0 6 11 17 (5.2%)
All feeding groups 86 (26.3%) 134 (41.0%) 107 (32.7%) 327 (100%)
Table 2 Maternal weekly hours spent in unpaid childcare and other domestic work, personal care and free time activities, combined
feeding groups
(a)
a. Activity/Breastfeeding status No breastfeeding
(b)
(obs = 27)
Any breastfeeding
(b)
(obs = 300)
p-value
Necessary time
Sleep, adult meals and other personal care time 65.48 63.43 .409
Maternal sleep 58.13 57.41 .085
Committed time
Childcare 39.39 47.89 .007
Sleeplessness 1.63 3.48 .029
Other unpaid work 21.51 17.72 .039
Free time 22.26 19.47 .286
Night-time (sleep plus disturbed sleep) 61.20 59.32 .379
b. Activity/Age of target infant (months) 3 months
(obs = 86)
6 months
(obs = 134)
9 months
(obs = 107)
p-value
Necessary time
Sleep, adult meals and other personal care time 64.18 65.59 63.58 .186
Sleep 55.79 57.32 55.65 .202
Committed time
Childcare 47.1 42.97 40.66 < 0.001
Sleeplessness 2.98 2.33 2.18 .135
Other unpaid work 17.77 20.31 20.70 .003
Free time 21.60 19.86 21.09 .342
Night-time (sleep plus disturbed sleep) 60.25 61.28 59.24 .154
(a)
Back- transformed means from residual maximum likelihood analysis, using linear mixed model.Note the back-transformed means will be similar, but not be
the same as the predicted means for the original data due to the square root transformation and the unbalanced nature of the data. See supplementary table for
predicted means and average standard error of difference.
(b)
No breastfeeding is exclusive formula feeding (feeding category B) & formula milk and solids (E)).
Any breastfeeding is exclusive breastfeeding (feeding category A), mixed breast milk and formula milk –no solids (C), breastmilk and solids (D), mixed breastmilk
and formula milk with solids (F))
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Table 2a shows that there were no significant differ-
ences in time spent asleep between lactating and non
lactating mothers (p= .085). Weekly hours of sleepless-
ness were greater for lactating mothers (p= .029). Lactat-
ing mothers spent 8.5 h more weekly in childcaring
activity (p= 0.007). As shown elsewhere [28], average
weekly employment hours were higher for lactating
mothers (2.7 vs. 1.2 h, p< 0.01), as were childcare hours
(47.89 vs 39.39, p< .01). There were no significant differ-
ences in free time between lactating and non lactating
mothers. As shown in Table 2a, in comparisons of lac-
tating with non-lactating women, other weekly unpaid
work was significantly higher for those not breastfeeding
compared to those who were breastfeeding (p= .039).
Mothers of older infants did not spend significantly
more or less time asleep than mothers of younger in-
fants (Table 2b, p= .13). Free time remained at around
20–21 h a week for all ages of infant. Mothers of older
infants spent significantly more hours on unpaid house-
work, around 3 additional hours weekly (p= .003), but
less on childcare (p< .001).
Maternal time use –sleep and free time comparisons for
detailed feeding groups
Table 3also comprises two parts a and b, and reports
predicted means for maternal time spent in various ac-
tivities. This table is by detailed infant feeding group,
and by infant age. The two parts are to be interpreted
similarly to Table 2.
Small cell sizes for formula fed infants (n=3, n=5,
n= 17), some of whom were also breastfed, suggest the
need for caution in interpreting differences, as differ-
ences between any particular detailed feeding group cat-
egories may or may not be statistically significant.
Hence, we discuss results only for comparisons where
cell size is large (see Table 1), and mean differences are
substantial.
Table 3a shows that unlike for comparisons between
combined feeding groups (reported in Table 2), there
were significant differences (p= .004) in maternal sleep
time of up to around 10 h a week between the 6 detailed
feeding groups. Those exclusively breastfeeding spent
the least time sleeping or napping (averaging 49.56 h
Table 3 Maternal weekly hours spent in unpaid childcare, personal care and free time activities, detailed feeding groups
(a)
a. Maternal weekly hours spent in activity, by detailed feeding group (for all target infant ages)
Activity/Breastfeeding status A. Breastfed
only (obs = 95)
B. Formula
only (obs = 5)
C. Breastfed &
formula fed
(obs = 3)
D. Breastfed &
solids (obs = 185)
E. Formula fed &
solids (obs = 22)
F. Breastfed &
formula fed &
solids (obs = 17)
p-value
Necessary time
Sleep, adult meals and other
personal care time
58.46 66.24 62.93 66.08 67.70 68.91 .024
Sleep 49.56 58.38 56.54 57.03 60.25 59.04 .004
Committed time
Childcare 49.48 38.79 41.43 47.60 38.09 43.31 .060
Sleeplessness 3.24 1.51 7.24 3.59 1.71 3.17 .222
Free time 20.66 19.87 21.10 18.99 22.01 17.01 .719
Night-time parenting
(sleep plus sleeplessness)
54.45 60.72 64.56 61.91 63.30 63.92 .008
b. Maternal weekly hours spent in activity, by age of target infant (for detailed feeding group)
Activity Age of target infant (months) p-value
3 (obs = 86) 6 (obs = 134) 9 (obs = 107)
Necessary time
Sleep, adult meals and other
personal care time
69.44 64.32 61.43 .006
Maternal sleep 60.87 55.98 53.52 .006
Committed time
Childcare 45.30 42.85 40.95 .239
Sleeplessness 3.94 2.95 2.72 .510
Free time 19.64 19.30 20.80 .445
Night-time parenting
(sleep plus sleeplessness)
66.60 52.85 49.90 .002
(a)
Back- transformed means from residual maximum likelihood analysis, using linear mixed model. Note the back-transformed means will be similar, but not be
the same as the predicted means for the original data due to the square root transformation and the unbalanced nature of the data. See supplementary table for
predicted means and average standard error of difference
Smith and Forrester International Breastfeeding Journal (2021) 16:7 Page 8 of 13
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
weekly, 7.08 h daily). Average hours committed to night-
time parenting, ‘sleeplessness’, were not significantly dif-
ferent between the feeding groups. As in the combined
feeding group analysis, there were also no statistically
significant differences in mothers’free time between
these detailed feeding groups.
Maternal sleep hours were significantly different by in-
fant age for the detailed feeding groups (Table 3b). Time
spent asleep by mothers was significantly less (p= .006)
if they had older infants. Analysis for detailed feeding
groups showed no significant differences in the mothers’
hours of ‘sleeplessness’for older babies compared to
younger babies. However, nighttime parenting hours de-
clined as there were reduced maternal hours of both
sleep and sleeplessness as infants got older (p= .002).
This suggests reduced conflict in time use between ‘ne-
cessary’hours of maternal of sleep and maternal hours
‘committed’to nighttime parenting as infants matured.
Mothers’time in childcaring activities, or enjoying free
time activities did not change significantly with infant
age when analysed for detailed feeding groups.
Maternal time use –statistical interaction of detailed
feeding group with target infant age
Testing using Wald statistics and approximate F-
statistics did not reveal statistically significant interac-
tions between target infant age and feeding group on
these maternal time use activities for combined feeding
groups (Table 2). However, for the detailed feeding
groups in Table 3infant feeding category did interact
significantly with age of infant for unpaid work hours.
We therefore calculated predicted means for this activity
to explore these interactions more fully (Table 4). (The
number of observations for each pairing is in Table 1.)
Table 4presents a more complex picture, allowing a po-
tentially more nuanced interpretation of the results in Ta-
bles 2and 3. Small cell sizes for mothers who were using
formula, especially in the early months (see Table 1), empha-
sise the need for caution in interpreting differences. Differ-
ences between any particular detailed feeding group or
infant age categories may or may not be statistically
significant. As noted earlier, in the combined analysis (Table
2a), unpaid domestic (house)work hours were significantly
greater for those that were not breastfeeding, and mothers of
older infants did significantly more unpaid housework than
mothers of younger (Table 2b). Table 4showing weekly un-
paid work hours for the detailed feeding groups reveals that
at three months, those who were exclusively breastfeeding as
recommended spent 16.02 h weekly on housework, and at
nine months, those still breastfeeding with solids as recom-
mended spent 19.25 h weekly doing housework. Results for
other feeding groups are more difficult to compare but the
interaction of infant age and detailed feeding group suggest
that maternal unpaid work burdens may be relevant for un-
derstanding relationships between optimal breastfeeding and
maternal sleep outcomes.
Discussion
This time use study of new mothers addressed questions
about whether maternal sleep hours are associated with
infant feeding method, and explored how sleep fitted
into mothers’daily work and leisure time for different
categories of infant feeding. Using a sample of Australian
breastfeeding and non-breastfeeding mothers with
broadly similar socioeconomic and demographic charac-
teristics, we used innovative statistical analysis tech-
niques to exploit opportunities offered by time use data
records providing week-long (cross sectional and re-
peated measures) observations of maternal activity at 3,
6 and 9 months of infant age. The first key finding is that
there were no significant differences in average hours of
sleep when comparing ‘breastfeeding’with ‘non-breast-
feeding’women, although breastfeeding involved more
time being ‘sleepless’at night.
A second key finding is that maternal free time for re-
creation and social activities did not differ significantly
between feeding groups, despite the varied night-time
parenting patterns. Thirdly, this study provides the first
analysis of maternal sleep alongside unpaid housework
activity. It found that lower hours were spent on unpaid
housework by lactating women, who spent more hours
instead on providing childcare. We interpret these
Table 4 Relationships between detailed feeding group and maternal sleep outcomes –statistical interaction with target infant age
(P= .039), maternal weekly hours(
a
}
Feeding group/Age of target infant 3 months 6 months 9 months
A. Breastfed only 16.02 16.84 13.51
B. Formula only 20.69 14.52
C. Breastfed & formula fed 16.08 23.46
D. Breastfed & solids 9.59 17.88 19.25
E. Formula fed &solids 25.96 22.53
F. Breastfed & formula fed & solids 26.05 17.08
(a)
Back- transformed means from residual maximum likelihood analysis, using linear mixed model. Note the back-transformed means will be similar, but not be
the same as the predicted means for the original data due to the square root transformation and the unbalanced nature of the data. See supplementary table for
predicted means and average standard error of difference
Smith and Forrester International Breastfeeding Journal (2021) 16:7 Page 9 of 13
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
results as suggesting that mothers adapted their daily
work commitments to prioritise some minimum free
time, but as infant age increased, mothers reduced child-
care hours and spent more time on unpaid domestic
work (or employment).
In our analysis by more detailed feeding group, exclu-
sive breastfeeding was associated with lower maternal
sleep hours, and surprisingly, the REML analysis showed
that maternal sleep hours were significantly lower for
those with older infants and more diversified infant feed-
ing practices. This emphasises that improved under-
standing of how infant sleep and feeding affects women
and night-time parenting may require categorising feed-
ing practices in detail, and not dichotomously. Also, the
relationship between infant feeding and unpaid domestic
work interacted significantly with infant age only in the
detailed feeding group analysis. This reflects that mater-
nal time on unpaid childcare and housework also
changes in complex ways as infants mature and as feed-
ing practices move away from exclusive breastfeeding
after the early months. Our analysis by detailed feeding
group showed that mothers who used formula during
the first 6 months spent more time on housework than
those who did not, but the causal direction is not clear.
We note that some cell sizes are not large enough to
draw strong inferences between detailed feeding groups.
Current research is focused on infant sleep, and indi-
cates conflicting results comparing infant sleep duration
for breastfeeding versus formula feeding. It indicates
generally less night waking and longer continued night
sleep in formula fed infants, though feeding-related sleep
differences are also associated with higher mortality in
formula fed infants such as SIDS, and morbidity includ-
ing wheezing problems [2,4,50]. Limitations of existing
research include firstly, that many studies do not disag-
gregate by detailed feeding method, and thus may in-
clude formula or mixed fed with partly breastfed infants.
The effect on infant sleep of feeding solids has also been
specifically investigated, with conflicting results reported
[4,5]. Secondly, some studies do not account for in-
creasing infant age on sleep duration and night waking
patterns; many do not examine whether differences in
sleep patterns are sustained past 6 months [2,3,6]. Dif-
ferences evident in studies of infant sleep by age point to
the importance of innate processes for sleep maturation
over time [21–23,50]. Mothers of older infants in this
study did not spend significantly more or less time
asleep.
Evolved mammalian behaviour involves potential ma-
ternal sleep behavioural and endocrinal adaptive mecha-
nisms postnatally [26,50]. As well, sleep of new mothers
and infants is shaped by cultural and social influences
on daily activity patterns and our study is novel in exam-
ining these. Such influences include cultural or gender
norms about infant sleep [20], and women’s leisure time,
or affecting family members’expectations about mater-
nal employment or unpaid work, and gendered alloca-
tions of responsibilities for earning income or caring for
young children.
Our study highlights that because infants require feed-
ing and care at night, new mothers experience substan-
tially lower and disrupted sleep hours compared to
norms evident in time use research for adult popula-
tions, where sleep is categorised as a ‘necessary’activity.
A recent OECD study of populations aged 15–64 found
that personal care, including sleeping and eating, ac-
counts on average for 46% (11 h) of a 24-h day or around
77 h a week [51]. The remaining time is spent on leisure
(20% of people’s total time, being 5 h a day, or around
34 h a week), and in employment or study (on average
19% of people’s time). This raises the question of
whether new mothers attempting conformity to unrealis-
tic social norms for adult sleep may induce changes in
feeding practice away from exclusive breastfeeding,
where prevailing social norms are inconsistent with bio-
logical norms for mother-infant dyads. By contrast, new
mothers’personal time was shown in this study to be
well below 70 h a week. Mothers’free time during the
post-natal months was also low by comparison at
around 20 h a week, again raising the question about
how maternal expectations about leisure may or may
not adapt to social norms.
The usual focus regarding infant care and feeding is on
child health and development. Time is increasingly recog-
nised as a resource needed to enable parents to provide
the nurturing care underpinning optimal early child devel-
opment. The recent Lancet series on child development
cited policies including parental leave and breastfeeding
breaks as key elements of evidence based approaches to
optimising early childhood development [52].
Access to time resources also has implications for
women’s health and well-being. Results from this study
bring into focus the demands on women’s time to meet
their own needs for sleep and leisure when they are car-
ing for an infant, regardless of feeding method. Interest-
ingly, in this study the unpaid work hours of new
mothers differed significantly by feeding group but this
interacted with infant age. Among breastfeeding mothers
the introduction of solids seems to increase unpaid work
hours as the infant got older, whereas in formula feeding
mothers, unpaid work hours reduced with infant age but
remained much higher than for breastfeeding mothers at
9 months. Relatedly, in previous research [28], maternal
employment hours also interacted statistically with in-
fant age and whether or not the mother was breastfeed-
ing. Help received from other family members with
infant care also did not differ by feeding group, and was
minimal for most mothers.
Smith and Forrester International Breastfeeding Journal (2021) 16:7 Page 10 of 13
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Such complex time use relationships point to potential
importance of paid or unpaid work commitments in con-
straining women’s capacity to adapt or adjust to reduced
sleep or leisure opportunities after the birth of an infant.
Together, these also suggest that gender equitable strategies
for adjusting to night-time parenting involves reducing ma-
ternal work (employment obligations or housework) com-
mitments, not only sharing infant care or feeding or
altering feeding regimes. At the time of the TUSNM, only
around 40% of new mothers took paid maternity leave, and
this averaged less than 3 months in duration [53].
Limitations
Our study has several limitations. It addressed maternal
time use including sleep, but did not measure outcomes,
or perceptions and expectations about sleep. Its general-
isability to different populations may be limited by self-
selection bias, as participation was voluntary. The small
sample size limits the conclusions that can be drawn
about the statistical significance of comparisons between
particular feeding subgroups. Sensitivity analyses of re-
sults in Table 4show that alternative statistical analysis
strategies of removing the non-breastfeeding groups (ex-
clusive formula feeding (B) and formula milk plus solids
(E)) or alternatively combining (groups exclusive formula
feeding (B) and mixed breast milk and formula no solids
(C)) did not alter our findings regarding statistically sig-
nificant variables or effects of feeding group or infant
age on predicted means. Findings regarding maternal
time use may not be generalizable to other countries. Al-
though study participants had broadly homogenous
socio-demographic characteristics, there is potential
confounding from missing variables, due to mothers
self-selecting into breastfeeding based on a complex
combination of personal and social characteristics. These
may include mental health variables such as anxiety or
depression, or the availability of social and health ser-
vices support, including for example paid maternity
leave [54]. Higher representation of better educated,
breastfeeding women in our sample may bias the results
if the sample differs markedly from the population at
large (such as in their degree of commitment to breast-
feeding notwithstanding potential sleep loss) in how in-
fant feeding and maternal sleep are linked. Reverse
causation is also possible for the associations identified
–the amount of time mothers allocate to personal care
activities including sleeping could determine their likeli-
hood of maintaining exclusive or partial breastfeeding,
rather than feeding practice determining maternal time
use such as that utilised for maternal sleep.
Future studies could explore whether endocrine fac-
tors may be implicated in different patterns of maternal
time use between mothers practicing different degrees of
breastfeeding.
Future research could also explore how equally the
hours of work (paid and unpaid) are distributed between
parents in the year after birth of an infant, how this is af-
fected by paid maternity leave access and duration, and
whether paternity leave increases gender equality in un-
paid domestic work, as distinct from childcare activities.
The extent to which access to sleep and leisure time is
socially patterned among new mothers is also an import-
ant area for investigation in larger, population-based
samples of families with children. The introduction of
the paid parental leave (PPL) scheme in Australia in
2011 and the forthcoming ABS TUS in 2020–21 pro-
vides the opportunity for such research.
Conclusions
New mothers experience reduced sleep hours, more
night-time parenting, and reduced time for personal
care, leisure and recreation activities compared to adult
norms, regardless of feeding method. The amount of
time taken to care for infants even older infants is sub-
stantial, and is likely to be intense. Where mothers ex-
perience less sleep hours, they may reallocate time from
less preferred activities such as paid employment and
unpaid domestic work to gain necessary personal and
free time. Flexibility to reallocate time this way as well as
providing time for nurturing care and breastfeeding of
the infant may also depend importantly on sharing paid
or domestic work responsibilities with others.
Recognising the temporal as well as the physiological
mechanisms by which maternal mental health and child
development benefit from policies and interventions
such as paid maternity leave may have important impli-
cations for the design and effectiveness of parental leave
and other social policies in promoting nurturing care
and feeding of infants. It may also inform practice and
program development by those supporting families with
infants and young children.
Supplementary Information
The online version contains supplementary material available at https://doi.
org/10.1186/s13006-020-00347-z.
Additional file 1: Table S2. Maternal weekly hours spent in unpaid
childcare and other domestic work, personal care and free time activities,
by no or any breastfeeding and by age of target infant
a)
Additional file 2: Table S3. Maternal weekly hours spent in unpaid
childcare, personal care and free time activities, by detailed feeding
group and by age of target infant
a)
.
Additional file 3: Table S4. Maternal weekly hours spent in other
unpaid work
a)
.
Abbreviations
ABS: Australian Bureau of Statistics; ANU: Australian National University;
ANOVA: Analysis of variance; REML: Residual maximum likelihood; TUS: Time
Use Survey; TUSNM: Time Use Survey of New Mothers
Smith and Forrester International Breastfeeding Journal (2021) 16:7 Page 11 of 13
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Acknowledgements
The assistance of Mark Ellwood, President of Pace Productivity in initial
design and conduct of the TUSNM is gratefully acknowledged. The authors
appreciate the important contribution of the new mothers participating in
the study. Research assistance and survey administration by Louise Bartlett is
also acknowledged.
Authors’contributions
JPS conceived and designed the study, collected the data, and wrote the
manuscript. RF assisted with design, performed the statistical analysis, and
critically reviewed the manuscript. The author(s) read and approved the final
manuscript.
Authors’information
JPS holds a PhD in Economics and BEc(Hons)/BA (Asian Studies) from the
Australian National University (ANU), and qualifications in breastfeeding
counselling and education. As an Australian Research Council (ARC) Future
Fellow, she was Professor (Associate) at the ANU School of Regulation and
Global Governance and the Research School of Population Health from 2015
to 2019. She is currently an honorary associate professor at the ANU College
of Health and Medicine, and ANU Fellow at the Crawford School of Public
Policy.
RIF (MSc, Dip Ed) held appointment as a statistical consultant at the ANU
Statistical Consulting Unit. He is currently is currently a visiting fellow at the
ANU.
Funding
Australian Research Council (DP0451117 and FT140101260). The funders had
no role in the design of the study; in the collection, analyses, or
interpretation of data; in the writing of the manuscript, and in the decision
to publish the results.
Availability of data and materials
The datasets used and/or analysed during the current study are available
from the corresponding author on reasonable request.
Ethics approval and consent to participate
All participants gave written informed consent before enrolment (Protocol
2005/51 approved on 10 March 2005 by the ANU Human Research Ethics
Committee under the National Statement on Ethical Conduct in Research
Involving Humans (1999).
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Research School of Population Health, College of Health and Medicine, The
Australian National University, Canberra, Australia.
2
Statistical Consulting Unit,
The Australian National University, Canberra, Australia.
Received: 19 October 2019 Accepted: 9 December 2020
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