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Cognitive impairment during pregnancy:
a meta-analysis
Sasha J Davies, Jarrad AG Lum, Helen Skouteris, Linda K Byrne, Melissa J Hayden
“Baby brain”refers to a subjective decline in cognition
reported by up to 81% of women who have been
pregnant.
1,2
Memory problems, reading difficulties,
confusion, disorientation, poor concentration, increased absent-
mindedness, and reduced motor coordination have been noted,
1,3-5
as has a general slowing of cognition; forgetfulness is the most
frequently cited change.
1
Similar deficits in broader cognitive
processes have also been reported, including in executive functions
and attention.
1-3
The impact of these deficits on everyday life can be significant. In
case study interviews, currently and recently pregnant women
have described a variety of real world consequences of “baby
brain”, including impaired conversational fluency at work and
home, greater reliance on note-taking for organising work and
domestic commitments, frequent forgetting of appointments, dif-
ficulties with reading comprehension, and even the inability to
return to work because of severe memory problems.
1
Objective confirmation of these perceived cognitive deficits during
pregnancy has, however, been equivocal, despite an accumulating
body of empirical research. While evidence of adverse cognitive
effects during pregnancy has been reported,
2,6-12
other
investigations have found little or no change.
3,13-15
This inconsis-
tency was also evident in the most recent meta-analysis of reports
on the impact of pregnancy on memory (2007),
16
which found
evidence for deficits in some, but not all, components of memory.
No recent meta-analysis of findings regarding pregnancy and
memory dysfunction has been published, nor has this relationship
been explored in cognitive domains apart from memory. Our pri-
mary aim was therefore to examine whether pregnancy is associ-
ated with differences in memory performance (compared with
non-pregnant women or with their own earlier performance), or
with differences in overall cognitive function, executive function,
and attention. Our second aim was to identify the specific gesta-
tional stages at which any differences emerge.
Methods
Study design
We undertook a meta-analysis of studies that have reported
quantitative relationships between pregnancy and changes in
cognition.
Eligibility criteria
Published studies were eligible for inclusion in our analysis if they
included:
a sample of healthy adult pregnant women and a control
group of healthy adult non-pregnant women;
at least one standardised objective measure of cognitive
function (eg, Wechsler Adult Intelligence Scale [WAIS]
subtasks); and
data appropriate for meta-analysis (eg, means with standard
deviations [SDs]).
Studies that included adolescent women (under 18 years of age) or
women with high risk pregnancies, or which exclusively employed
customised, naturalistic, or self-reported cognitive measures were
excluded. There were no restrictions with regard to gestational
trimester, parity, socio-economic status, or ethnic background. All
included studies were published in peer review journal, without
restriction on publication date.
Information sources and study selection
We searched three databases —Cumulative Index to Nursing
and Allied Health Literature (CINAHL) Complete, MEDLINE
Complete, and PsychINFO —for a panel of terms and their
Abstract
Objectives: Many women report declines in cognitive function
during pregnancy, but attempts to empirically evaluate such
changes have yielded inconsistent results. We aimed to
determine whether pregnancy is associated with objective
declines in cognitive functioning, and to assess the progression
of any declines during pregnancy.
Study design: We undertook a meta-analysis, applying a
random effects model, of 20 studies that have reported
quantitative relationships between pregnancy and changes in
cognition.
Data sources: Full text articles indexed by Cumulative Index to
Nursing and Allied Health Literature (CINAHL) Complete,
MEDLINE Complete, and PsychINFO.
Data synthesis: The 20 studies assessed included 709 pregnant
women and 521 non-pregnant women. Overall cognitive
functioning was poorer in pregnant women than in non-pregnant
women (standardised mean difference [SMD], 0.52 [95% CI,
0.07e0.97]; P¼0.025). Analysis of cross-sectional studies
found that general cognitive functioning (SMD, 1.28 [95% CI
0.26e2.30]; P¼0.014), memory (SMD, 1.47 [95% CI, 0.27e2.68];
P¼0.017), and executive functioning (SMD, 0.46
[95% CI, 0.03e0.89]; P¼0.036) were significantly reduced
during the third trimester of pregnancy (compared with control
women), but not during the first two trimesters. Longitudinal
studies found declines between the first and second
trimesters in general cognitive functioning (SMD, 0.29 [95% CI,
0.08e0.50]; P¼0.006) and memory (SMD, 0.33 [95% CI,
0.12e0.54]; P¼0.002), but not between the second and
third trimesters.
Conclusions: General cognitive functioning, memory, and
executive functioning were significantly poorer in pregnant than
in control women, particularly during the third trimester. The
differences primarily develop during the first trimester, and are
consistent with recent findings of long term reductions in brain
grey matter volume during pregnancy. The impact of these
effects on the quality of life and everyday functioning of
pregnant women requires further investigation.
Deakin University, Melbourne, VIC. m.hayden@deakin.edu.au jdoi: 10.5694/mja17.00131
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combinations, including “pregnan*”,“cogniti*”, and “reward
seek*”(full list in the online Appendix). The date of the final search
was 11 November 2016. Two authors (SD, MH) screened the
abstracts of articles for eligibility, and disagreements (< 5%) were
resolved by discussion. Article reference lists were screened for
additional relevant records.
Study quality and characteristics
The methodological quality of the studies included in the
meta-analysis was assessed with a modified version of the
NewcastleeOttawa Scale for cohort studies.
17
SD and MH inde-
pendently assessed the quality of all included articles; no studies
were excluded by the quality assessment.
Data extraction and effect size calculations
From each article we extracted data on author, publication year,
sample size, study design, gestational trimester, age, parity, and
measure scores (mean, SD). The effect size in our analysis was the
standardised mean difference (SMD); that is, the difference
between the pregnant and control women groups for a given
outcome variable, expressed in standard deviation units. Effect
sizes were computed for general cognitive functioning, and for the
three primary cognitive domains: memory, attention, and execu-
tive functioning. For cross-sectional data, positive SMD values
indicated that the performance of the control group was superior to
that of the pregnant women group; for longitudinal studies, posi-
tive values indicated that the cognitive performance of pregnant
women was superior at the later of two compared assessments.
Summary data from statistical tests were extracted to calculate the
SMD and its variance. For 18 studies, these values were calculated
from the reported means and SDs.
2,7,10,12,14,15,18-29
We contacted
the authors of eight studies for which these data were not reported,
but which were otherwise eligible for inclusion. The authors of two
provided the additional data, and the studies were included in our
analysis.
30,31
Of the remaining six studies, the authors responded in
two cases that they no longer had access to the data;
3,11
we received
no response regarding the other four studies.
6,8,32,33
A random effects model weighted individual studies to compute
an average effect size for all studies. The model assumed that dif-
ferences between study-level effect sizes reflected the contribution
of within-study error and of sampling and systematic influences
(true heterogeneity).
34
Systematic influences may arise from study-
level differences in participant characteristics (eg, age, gestational
stage, parity), the aspects of cognitive functioning assessed, and
differences in methodological quality. The I
2
statistic was calcu-
lated; it quantifies the heterogeneity between individual studies as
a percentage (25% ¼low, 50% ¼moderate, 75% ¼high levels of
systematic heterogeneity).
35
To assess potential bias in the report-
ing of effects, a fail-safe N (ie, the number of additional studies with
an effect size of zero that would need to be found to render the
overall effect size for the studies included in the meta-analysis non-
significant) was also calculated.
For cross-sectional studies of subgroups of pregnant women
(trimester 1 [T1], T2, T3), the subgroups were collapsed to a single
pregnant women group for initial analyses comparing the perfor-
mance of pregnant and non-pregnant women by computing a
weighted average mean and SD for the cognitive task scores. Each
subgroup was then separately compared with the non-pregnant
control women.
In longitudinal studies of cognitive performance across pregnancy
included in our meta-analysis, correlations between effect sizes
were not reported. We therefore estimated effect size correlations
at r¼0.5 for each study; each trimester was separately compared
with each of the other two trimesters.
Results
Study selection
After removing duplicates, the initial search identified 3805
records, of which 3734 were excluded as irrelevant after screening
their titles and abstracts. The full texts of the remaining 71 records
were assessed for suitability, and 26 articles were deemed relevant;
of these, sufficient data were available for twenty (see paragraph 2
of “Data extraction”for details) to include them in our meta-
analysis (Box 1). The 20 studies included a total of 709 pregnant
women and 521 non-pregnant women.
Study characteristics and quality assessment
The sample size, participant characteristics, study design, and the
cognitive tasks assessed in each study and the methodological
quality of each study are summarised in the online Appendix.In17
of 20 studies, the pregnant women and control groups were
matched by age and education or IQ level. Eight studies included
a follow-up assessment, with four allowing an inter-assessment
interval of longer than 12 weeks. The fail-safe N indicated that
210 additional studies with non-significant effect sizes would be
required for the difference in overall cognitive performance
1 Preferred Reporting Items for Systematic Reviews and
Meta-Analyses (PRISMA) outline of the selection of
articles for inclusion in our meta-analysis
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between pregnant and control women to be statistically non-
significant (ie, P> 0.05).
General cognitive functioning
We defined general cognitive functioning broadly as encompass-
ing a range of processes, including memory, attention, executive
functioning, processing speed, and verbal and visuospatial abili-
ties (online Appendix, table 1).
Effect sizes and weighted averages for all 20 studies comparing the
general cognitive performance of pregnant and non-pregnant
women were calculated. Overall cognitive functioning was
poorer in pregnant women than in non-pregnant women (SMD,
0.52 [95% CI, 0.07e0.97]; P¼0.025; I
2
¼91%).
Additional between-groups analyses were conducted to identify
the specific gestational stage at which cognitive performance
changes in pregnant women. There was no significant differences
in cognitive functioning between pregnant women during T1 and
controls (four studies: SMD, 0.84 [95% CI, e0.47 to 2.15]; P¼0.21;
I
2
¼94%), nor between pregnant women during T2 and controls
(three studies: SMD, 1.25 [95% CI, e0.83 to 3.34]; P¼0.24;
I
2
¼96%) (data not shown). Cognitive functioning in women
during T3 was significantly poorer than that of control women
(six studies: SMD, 1.28 [95% CI, 0.26e2.30]; P¼0.014; I
2
¼93%)
(Box 2).
Four longitudinal studies reported effect sizes for changes in
overall cognitive performance between T1 and T2; the difference
was significant, with no heterogeneity (SMD, 0.29 [95% CI,
0.08e0.50]; P¼0.006; I
2
¼0%) (Box 3). In contrast, differences
between T2 and T3 (six studies: SMD, 0.11 [95% CI, e0.18 to 0.39];
P¼0.46; I
2
¼64%) and between T1 and T3 (five studies: SMD,
e0.13 [95% CI, e0.65 to 0.39]; ; P¼0.63; I
2
¼88%), were non-
significant (data not shown).
Memory
We defined memory as encompassing a range of subdomains,
including working memory and retrieval from long term memory
via recognition and recall. The 19 studies that assessed memory
applied a range of measures, including several WAIS tasks (eg,
digit span backwards and forwards) as well as a broad selection of
other recall and recognition tasks (eg, facial recognition sets, the
Rivermead behavioural memory task, visualeverbal learning
tasks). Overall memory performance was significantly lower in
2 General cognitive functioning: comparison of pregnant women in their third trimester with non-pregnant control women
(studies reporting between-group comparisons)
CI ¼confidence interval; SMD ¼standardised mean difference. u
3 General cognitive functioning: comparison of pregnant women in their first and second trimesters (studies reporting
within-group comparisons)
CI ¼confidence interval; SMD ¼standardised mean difference. u
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pregnant than in non-pregnant women (SMD, 0.48 [95% CI,
0.04e0.92]; P¼0.033; I
2
¼91%).
Cross-sectional studies comparing the memory performance of
pregnant women at each gestational trimester with control women
found significantly lower values for pregnant women during T3
(five studies: SMD, 1.47 [95% CI, 0.27e2.68]; P¼0.017; I
2
¼94%)
(Box 4), but not during T1 (four studies: SMD, 0.84 [95% CI, e0.47 to
2.15]; P¼0.21; I
2
¼94%) or T2 (three studies: SMD, 1.17 [95% CI,
e1.04 to 3.38]; P¼0.30; I
2
¼97%) (data not shown). There was a
high degree of heterogeneity between studies for each comparison.
Longitudinal studies comparing memory performance at different
stages of pregnancy found a significant reduction in performance
between T1 and T2, with negligible heterogeneity between studies
(four studies; SMD, 0.33 [95% CI, 0.12e0.54]; P¼0.002; I
2
¼0%)
(Box 5), but not between T1 and T3 (five studies: SMD, e0.20
[95% CI, e0.73 to 0.34]; P¼0.48; I
2
¼0%) or between T2 and T3 (six
studies: SMD, 0.12 [95% CI, e0.17 to 0.42]; P¼0.41; I
2
¼0%) (data
not shown).
Executive functioning and attention
Executive functions, mediated by the frontal cortex, include
attention, planning, shifting between ideas (flexibility), generating
new responses (fluency), problem-solving, and abstraction, as well
as the ability to inhibit inappropriate responses. The nine studies
that assessed executive functions applied a range of measures,
including the Cambridge Neuropsychological Test Automated
Battery intra-/extra-dimensional shift task, the concept shifting
test, and the paced auditory serial addition test. Attention refers to
both the initial orientation of attention and sustained attention
towards a given stimulus, and is included as a subset of executive
functioning processes. Tasks utilised by the eight studies to assess
attention included the test of everyday attention, the letter
cancellation task, and the Stroop task.
Effect sizes were calculated for cross-sectional studies that
compared executive functioning (nine studies) or attention (eight
studies) in pregnant and control women. The averaged effect sizes
for these studies were small and non-significant (executive func-
tioning: SMD, e0.12 [95% CI, e0.52 to 0.28]; P¼0.54; attention:
SMD, e0.22 [95% CI, e0.70 to 0.26]; P¼0.37).
Two cross-sectional studies compared attention and executive
functioning during T3 with those of controls;
10,14
while the effect
size for executive functioning was significant (SMD, 0.46 [95% CI,
0.03e0.89]; P¼0.036; I
2
¼0%) (Box 6), that for attention was not
(SMD, 0.37 [95% CI, e0.06 to 0.80]; P¼0.09). One study compared
attention and executive functioning during T2 with those of con-
trols,
14
but found no significant differences (executive functioning:
4 Memory functioning: comparison of pregnant women in their third trimester with non-pregnant control women
(studies reporting between-group comparisons)
CI ¼confidence interval; SMD ¼standardised mean difference. u
5 Memory functioning: comparison of pregnant women in their first and second trimesters (studies reporting within-group
comparisons)
CI ¼confidence interval; SMD ¼standardised mean difference. u
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SMD, 0.32; P¼0.26; attention: SMD, 0.30; P¼0.30). No studies
compared attention or executive functioning of women during T1
with those of control women.
Longitudinal studies comparing attention and executive func-
tioning in pregnant women at different stages of pregnancy found
no significant differences. One study reported non-significant
effect sizes for differences in executive functioning and attention
changes between T1 and T2 (executive functioning: SMD, 0.11;
P¼0.61; attention: SMD, 0.21; P¼0.31).
12
Two studies provided
data that permitted us to calculate the effect size for changes in
attention between T2 and T3;
12,14
neither was significant (executive
functioning: SMD, 0.07; P¼0.68; attention: SMD, 0.10; P¼0.53).
One study provided data that permitted us to calculate the effect
sizes for changes in attention between T1 and T3;
12
each was small
and non-significant (executive functioning SMD, 0.02; P¼0.94;
attention: SMD, 0.03; P¼0.89).
Discussion
Many, but not all, women report increased forgetfulness and
reduced cognitive functioning during pregnancy. We applied a
meta-analytic quantitative approach to investigating the associa-
tion between pregnancy and changes in cognitive functioning, and
reached two major conclusions. First, the general cognitive func-
tioning, memory, and executive functioning performance of
pregnant women is significantly lower than in non-pregnant
women, both overall and particularly during the third trimester.
Secondly, the memory performance of pregnant women appears to
decline between the first and second trimesters.
These findings are consistent with those of the 2007 meta-analysis
by Henry and Rendell.
16
But our meta-analysis also identified
further impairments of general cognitive and executive func-
tioning in pregnant women, and that there are also differences
between trimesters. Specifically, memory performance declined
during the early stages of pregnancy, but the decline either slowed
or stopped from mid-pregnancy. Moreover, the magnitude of the
changes in overall cognition and memory during the third
trimester of pregnancy is not only statistically, but also clinically
significant.
Given the small to moderate effect sizes of the differences and the
limited number of longitudinal studies available, our findings need
to be interpreted with caution, particularly as the declines were
statistically significant, but performance remained within the
normal ranges of general cognitive functioning and memory. These
small reductions in performance across their pregnancy will be
noticeable to the pregnant women themselves and perhaps by
those close to them, manifesting mainly as minor memory lapses
(eg, forgetting or failing to book medical appointments), but more
significant consequences (eg, reduced job performance or impaired
ability to navigate complex tasks) are less likely. However, the
available literature is highly heterogeneous; further research is
required to elucidate more clearly the impact of these changes on
the everyday life of pregnant women.
Our meta-analysis has two important strengths. First, by adopting
a quantitative meta-analytic approach it was possible to estimate
the influence of artificial variance by examining systematic vari-
ables in the presence of highly heterogeneous results. A medium to
high degree of heterogeneity between studies was found, with a
mean I
2
for studies with significant effect sizes of 61.5%. In
response, we employed meta-regression to examine whether
participant characteristics influenced each comparison (data not
reported here). While participant age was found to be a non-
significant source of artificial variance, other potential sources of
systematic influence (eg, parity, education, pre-partum IQ, socio-
economic status, study task selection) could not be explored
because the necessary data were not available. Nevertheless, the
fail-safe N indicated that 210 additional studies with zero effect
sizes would be required to abrogate the significance of the overall
difference, indicating that the findings of our meta-analysis are
robust despite the degree of study heterogeneity.
Second, both the total sample size and the effect sizes were larger
than in previous meta-analyses. We included nine studies pub-
lished since the 2007 review by Henry and Rendell,
16
encompass-
ing an additional 312 pregnant and 162 non-pregnant women
(76% and 45% increases respectively). This resulted in a substantial
increase in the magnitude of the effect sizes for changes in memory
performance. Most of the individual studies included in our meta-
analysis had relatively small sample sizes compared with the
cumulative total, and would not have adequate power to detect
effect sizes of the magnitude we found. However, comparisons of
performance in the domains of attention or executive functioning
were limited to a cumulative total sample of 105 pregnant women
and 82 non-pregnant controls across a maximum of two studies per
comparison, so that effect sizes were small. Consequently, confi-
dent conclusions can be drawn only with respect to the effect of
pregnancy on memory. Further research may establish whether
subtler impairments in other cognitive domains might be detectable.
Our review provides novel insights into the impact of pregnancy
on cognitive functioning, particularly memory and executive
functioning. While Henry and Rendell
16
concluded that processes
requiring active memory processing (eg, working memory and
6 Executive functioning: comparison of pregnant women in their third trimester with non-pregnant control women (studies
reporting between-group comparisons)
CI ¼confidence interval; SMD ¼standardised mean difference. u
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recall) appeared to be selectively impaired in pregnant women,
analyses we have undertaken (not reported here) indicate that
memory performance was significantly affected even when
working memory was isolated from other facets of memory. This
suggests that pregnancy may be associated with declines across
broader memory functions, not just working memory. This
conclusion is further supported by the results of a recently pub-
lished longitudinal neural imaging study which found that preg-
nancy was significantly associated with reduced grey matter
volume in brain regions involved in social cognition.
36
While our meta-analysis builds on past research by identifying the
gestational trimester during which cognitive deficits may develop,
it remains unclear whether these impairments are exacerbated by
increasing parity, or whether memory and executive functioning
return to pre-partum performance levels after giving birth.
Uncertainty about the precise mechanisms underlying these defi-
cits also persists, and about whether these diminutions of function
are equivalent to those observed in neurological or psychiatric
conditions associated with poorer performance in memory
domains requiring active processing.
In summary, our meta-analysis identified that performance related
to memory and executive functioning was significantly poorer in
pregnant than in control women, particularly during the third
trimester. It is recommended that future research adopt a longi-
tudinal design to clarify the progression of these cognitive
differences during pregnancy, and to establish their impact on the
day-to-day cognitive functioning of pregnant women.
Competing interests: No relevant disclosures. n
ª2018 AMPCo Pty Ltd. Produced with Elsevier B.V. All rights reserved.
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