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Memory Performance, but not Information Processing Speed, may be
Reduced During Early Pregnancy
R. H. M. de Groot; G. Hornstra; N. Roozendaal; J. Jolles
To cite this Article de Groot, R. H. M. , Hornstra, G. , Roozendaal, N. and Jolles, J.(2003) 'Memory Performance, but not
Information Processing Speed, may be Reduced During Early Pregnancy', Journal of Clinical and Experimental
Neuropsychology, 25: 4, 482 — 488
To link to this Article: DOI: 10.1076/jcen.25.4.482.13871
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2003, Vol. 25, No. 4, pp. 482–488 # Swets & Zeitlinger
Memory Performance, but not Information Processing Speed,
may be Reduced During Early Pregnancy
R.H.M. de Groot1,2, G. Hornstra2, N. Roozendaal3, and J. Jolles3
Department of Human Biology, Maastricht University, The Netherlands, 2Nutrition and Toxicology Research Institute Maastricht
(NUTRIM), Maastricht University, The Netherlands, and 3Department of Psychiatry & Neuropsychology,
Division of Cognitive Disorders, Brain & Behaviour Institute, Maastricht University, The Netherlands
Several studies have investigated aspects of cognitive functioning during late pregnancy or in the period
around delivery. The present paper describes a controlled study of neurocognitive functioning in an early
phase of pregnancy (14 weeks). Seventy-one pregnant women and 57 control subjects matched for age and
education were tested with a cognitive test battery. Intentional learning was tested with the Verbal Learning
Test, retrieval from semantic memory with the Fluency Test, and speed of information processing with the
Concept Shifting Test, the Stroop test, and the Letter Digit Substitution Test. Results show that performance
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on tests measuring intentional learning and retrieval from semantic memory were lower in the pregnant
group during early pregnancy as compared to a closely matched nonpregnant group. In contrast, speed of
information processing was not different between the two groups. The differences observed in memory
performance were not large and further research is needed to establish their clinical signiﬁcance. In addition,
the results should be interpreted with care, because our study has a cross-sectional design, which has
limitations concerning the fact that preexisting performance differences might be possible. Therefore,
longitudinal studies are essential to ascertain clear associations between pregnancy and cognitive
INTRODUCTION positive effect on some cognitive functions
(Christensen, Poyser, Pollitt, & Cubis, 1999; for
Forgetfulness and changed attentional functions review see Brett et al.; Brett & Baxendale, 2001).
have frequently been reported by pregnant These discrepant ﬁndings may be due to differ-
women (Condon, 1987). The majority of studies ences in the cognitive tasks used, or differences in
have reported decreased performance on neuro- the stage of pregnancy of the subjects investi-
cognitive tasks during pregnancy (e.g., Brindle, gated. Thus, there is no consistent answer to the
Brown, Brown, Grifﬁth, & Turner, 1991; question whether or not cognitive functioning is
Buckwalter et al., 1999; Eidelman, Hoffmann, affected during pregnancy.
& Kaitz, 1993; Parsons & Redman, 1991; Poser, Most of the above-mentioned studies investi-
Kassirer, & Peyser, 1986; Sharp, Brindle, Brown, gated only one or some aspects of cognitive
& Turner, 1993; Silber, Almkvist, Larsson, & functioning, and only two studies investigated
Uvnas-Moberg, 1990), but some have found no whether cognitive functioning is altered in an
effect of pregnancy (e.g., Morris, Toms, Easthope, early stage of pregnancy (Keenan, Yaldoo, Stress,
& Biddulph, 1998; Schneider, 1989) or even a Fuerst, & Ginsburg, 1998; Sharp et al., 1993). The
Address correspondence to: R.H.M. de Groot, Department of Human Biology, Maastricht University, P.O. Box
616, 6200MD Maastricht, The Netherlands. Tel.: þ 31 433881507. Fax: þ 31 433670976. E-mail:
Accepted for publication: September 23, 2002.
MEMORY PERFORMANCE 483
possibility that early pregnancy is already char- normal health, that is, not suffering from any metabolic,
acterized by cognitive changes is of importance as cardiovascular, renal, psychiatric, or neurological dis-
there is not yet a profound change in psychosocial orders. Exclusion criteria were diastolic blood pressure
higher than 90 mmHg, multiple pregnancy, consump-
circumstances around the pregnant woman. Pos- tion of dietary supplements rich in polyunsaturated fatty
sible changes in cognitive functioning could acids, and not being of Caucasian origin, in order to
therefore more directly be ascribed to biological limit scatter of the measuring results due to large
changes in the body brought about by hormones or differences in genetic, social, and cultural patterns.
by a redistribution of nutrients essential for brain The nonpregnant women in the control group were
functioning (e.g., long chain highly unsaturated friends or family members of the pregnant women, or
were recruited by advertisements in local newspapers.
essential fatty acids) in favor of the unborn child.
All in- and exclusion criteria were the same as for the
The present study investigated whether cogni- pregnant population with exception of the pregnancy-
tive functioning is different during early preg- related criteria. Their last pregnancy, if any, was at least
nancy (14 weeks after the last menstrual period) 32 weeks before study entry and if they had been
and, if so, whether speciﬁc cognitive functions are pregnant before, they were not breastfeeding during the
affected. A controlled design was chosen in which study.
pregnant women were compared to carefully Seventy-one pregnant women and 57 control
subjects volunteered to participate in this study. Groups
matched controls, and where performance of
were matched for age and education (measured on an 8-
memory tasks was compared to performance on point scale, ranging from primary education to higher
tests of information processing. The aspects of vocational training and university; Bie, 1987). All tests
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cognition we measured in this study were were administered in the subject’s home, in a situation,
focussed on memory and speed of information which enables testing under favorable conditions.
processing. The reason for this choice was that The study was approved by the Medical Ethics
pregnant women complain about concentration Committee of the University Hospital Maastricht and
written consent was obtained from each participant.
problems and everyday forgetting in particular
(Baildam, 1991; Kane, Harman, Keeler, & Ewing,
1968; Parsons & Redman, 1991; Welch, 1991). Tests for Cognitive Functioning
Sensitive tests are needed in order to detect
changes in cognition during pregnancy with Visual Verbal Word Learning Task (WLT)
reliability and validity, because such a study To assess learning capacity as well as recall and
concerns a healthy population, where there is no retrieval from long-term memory, a visual verbal word
learning task (Brand & Jolles, 1985) was completed by
reason to expect profound changes in cognitive
the subjects, according to the protocol of the MAAS
performance. The tests we decided to use, have study (Jolles, Houx, van Boxtel, & Ponds, 1995). This
already shown their effectiveness in earlier test is an improved version of a test originally devised
research into neurocognitive functioning in by Rey (Rey, 1964). Fifteen words were presented one
healthy subjects and in subjects with only mild after the other at 2-s intervals. After presentation, the
cognitive complaints (Engelberts et al., 2002; participants were asked to recall as many words as
Houx, 1991; van Boxtel et al., 1998). possible in any order. This procedure was repeated
three times. After 20 min (within this time the tasks
mentioned below were performed), delayed recall was
measured. Dependent variables were the mean recall
MATERIALS AND METHODS over three trials (WLTtot) and the delayed recall
(WLTdr) after 20 min. Four different test versions were
Subjects used across the population to prevent exchange of the
Pregnant women were recruited by midwives in the words, used in the test between family and friends in
region Maastricht, Heerlen, and Sittard, located in our test population. The test versions used in the Words
the south-eastern part of the Netherlands, and by the Learning Test were parallel test versions. The words in
Departments of Obstetrics and Gynecology of hospitals the lists consisted of frequently used meaningful
in the same area (University Hospital Maastricht, monosyllabic nouns matched for word frequency. All
Atrium Medical Center in Heerlen, and Maasland versions contained the same amount of living versus
Hospital in Sittard). The selection criteria for study nonliving words, the words were emotionally neutral
entry were a gestational age less than 14 weeks, and a and had on average the same amount of letters.
484 R.H.M. DE GROOT ET AL.
Concept Shifting Test (CST) in a random order. On the rest of the page, boxes are
The Concept Shifting Test (CST) was used to measure presented with just letters. Subjects were asked to ﬁll in
visual conceptual and visuomotor tracking (Houx, as many corresponding numbers as possible within
1991; Vink & Jolles, 1985). This test consists of four 1 min. The total number of digits correctly related to a
test sheets. On each test sheet, 16 small circles are letter was used as the dependent variable.
grouped in a larger circle. On the ﬁrst sheet, numbers
appear in a ﬁxed random order, on the second sheet Statistics
letters, and on the third sheet both. Subjects were One pregnant subject did not have reliable test results,
requested to cross out the items in the right order (1-2- because the conditions under which she performed the
3-4 (Subtask I), A-B-C-D (Subtask II), 1A-2B-3C cognitive tests were unacceptable. Data for this person
(Subtask III), respectively); the time required to do this were excluded from the analyses. Individual data were
was measured with a stopwatch. A fourth sheet with screened for extreme values based on normative data
empty circles (Subtask IV), which had to be crossed out from the Maastricht Aging Study (van Boxtel et al.,
as fast as possible, was used to correct for motor speed. 1998); Five datapoints were considered outliers, with
Mean speed for Subtasks I and II, corrected for motor values outside the range of þ /À 3*SD, and were
speed (Subtask IV), was used as a measure of general excluded from the analyses.
information processing speed. Subtask III, also cor- Subject characteristics were examined for statistical
rected for motor speed, was used as a measure of differences between the two groups by unpaired t tests.
concept shifting ability. The Mann–Whitney U-test analyzed the differences
in education and number of pregnancies. The group
Fluency (FLU) differences for the dependent variables were analyzed
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The subjects completed a ﬂuency task (Lezak, 1995) as by ANOVA with education and total number of
a measure of retrieval from long-term semantic pregnancies as covariates. In the analysis of the WLT
memory. Subjects had to name as many animals as a correction for test version was applied too. The CST
possible within 1 min. Fluency is a measure of the was also analyzed by a two-way ANOVA for group Â
adequate, strategy-driven retrieval of information from repeated measures (two variables), to ﬁnd out whether
semantic memory. The number of animals named was there was a differential effect for concept shifting (CST
used as dependent variable. III) or general speed (mean CST I/II). The same was
done for the Stroop test. A p level of < .05 was con-
Stroop Color-Word Interference Test sidered statistically signiﬁcant.
The Stroop Color-Word Interference Test was used to
test selective attention (Klein, Ponds, Houx, & Jolles,
1997; Stroop, 1935). The test involves three cards RESULTS
displaying 40 stimuli each: color names printed in black
(Subtask I), colored patches (Subtask II), and color
names printed in one of the other colors (Subtask III). Subject Characteristics
For Subtask I subjects had to read aloud the printed Table 1 shows the subject characteristics. With an
items, for Subtask II they had to name to color of the unpaired t test no statistically signiﬁcant differ-
patches and for Subtask III they had to name the ink ences were found between the two groups for age,
color the words were printed in. The amount of extra height, and weight. The control subjects tended to
time needed to discard irrelevant but very salient have attained a higher level of education
information (reading) in favor of a less obvious aspect
(p ¼ 0.0628). We therefore decided to use a sta-
(color naming) was recorded. Mean speed for Subtasks
I and II was used as a measure of general information tistical design in which education was controlled
processing speed. Subtask III was used as a measure of for. The average total number of pregnancies was
color word interference susceptibility. statistically different between the two groups
(p ¼ .0014). Therefore, we corrected for both
Letter-Digit-Substitution-Test (LDST) education and total number of pregnancies.
The Letter-Digit-Substitution-Test (LDST) is related to
the Symbol-Digit Modalities Test developed by Smith
Intentional Learning Task and Retrieval
(Smith, 1968), which originates from the Digit Symbol
Test developed by Wechsler (Wechsler, 1958). The from Semantic Memory
LDST was used to measure the efﬁciency of operations The control group had a signiﬁcantly higher score
in working memory. At the top of the test sheet, a box is on the WLTtot (mean Æ SD 11.77 Æ 1.34, n ¼ 57)
presented with nine numbers coupled with nine letters than the pregnant group (11.07 Æ 1.35, n ¼ 70,
MEMORY PERFORMANCE 485
Table 1. Subject Characteristics (Mean Æ SD).
Characteristics Pregnant group Control group
(n ¼ 71) (n ¼ 57)
Age (year)1 29.5 Æ 3.7 30.5 Æ 4.2
Education2 3.9 Æ 1.5 4.4 Æ 1.2
Height (cm) 168 Æ 5 168 Æ 6
Weight (kg) 70.15 Æ 14.86 70.27 Æ 13.94
Number of pregnancies* n (%) n (%)
0 0 (0) 17 (29.8)
1 25 (35.2) 11 (19.3)
2 31 (43.7) 17 (29.8)
3 9 (12.7) 8 (14.0)
>3 6 (8.4) 4 (7.1)
Note. 1The age range is 21–39 years.
Education was measured on an 8-point scale.
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Table 2. Cognitive Test Performance in the Pregnant Group Versus the Control Group (Mean Æ SD).
Tests Pregnant group Control group p
n ¼ 71 n ¼ 57
WLTtot (# words recalled) 11.07 Æ 1.35 11.77 Æ 1.34 .015*
WLTdr (# words recalled) 11.69 Æ 2.06 12.75 Æ 1.83 .006*
Fluency (# words/min) 24.80 Æ 5.46 27.84 Æ 5.79 .006*
CST (I þ II)/2 (s) 12.89 Æ 3.13 12.24 Æ 3.13 .421
CST (III) (s) 20.68 Æ 6.21 18.88 Æ 5.42 .303
Stroop (I þ II)/2 (s) 17.09 Æ 2.64 16.52 Æ 2.29 .872
Stroop (III) (s) 33.10 Æ 5.44 31.67 Æ 7.05 .491
LDST (# numbers ﬁlled in/min) 40.69 Æ 6.31 42.32 Æ 6.59 .624
Note. Differences between the pregnant group and the control group were corrected for education levels and total
number of pregnancies. WLT was also corrected for test version. WLT ¼ Words Learning Test, tot ¼ total
(mean of trial I, II and III) dr ¼ delayed recall, CST ¼ Concept Shifting Test, LDST ¼ Letter Digit
p ¼ .015). The same was found for WLT delayed Speed of Information Processing
recall task: 12.75 Æ 1.83 for the control group General speed of processing and concept shifting
(n ¼ 57) versus 11.69 Æ 2.06 for the pregnant in the concept shifting test were not different
group (n ¼ 70, p ¼ .006) (see Table 2). between the two groups (see also Table 2). Two
With respect to retrieval from long-term scores on this test were analyzed; the mean of
semantic memory, the pregnant group had a Version I and II as the general speed of informa-
signiﬁcantly lower score for the ﬂuency test than tion processing (p ¼ .421) and the score of Ver-
did the control group (24.80 Æ 5.46, n ¼ 70 vs. sion III as a measure of concept shifting ability
27.84 Æ 5.79, n ¼ 57; p ¼ .006 after correction for ( p ¼ .303). By two-way repeated measures
education and number of pregnancies). ANOVA no differential effect was found for
Analyses without correction for number of concept shifting.
pregnancies revealed comparable results (WLTtot Likewise, there were no signiﬁcant group
p ¼ .013, WLTdr p ¼ .004, FLU p ¼ .020). differences in scores on the Stroop test (p ¼ .872
486 R.H.M. DE GROOT ET AL.
for the group differences concerning the mean of (Keenan et al., 1998; Sharp et al., 1993). In our
Stroop Version I and II and p ¼ .491 for Ver- study, explicit memory (as measured by WLTtot
sion III). Also, two-way ANOVA for repeated and WLTdr) was signiﬁcantly impaired in the
measures did not show any statistically signiﬁcant pregnant group compared to the control group.
differences. Finally, scores on the Letter Digit These results are consistent with those of Keenan
Substitution Test were not statistically different et al. (1998), who, however, only found statisti-
between the pregnant and the control groups cally signiﬁcant differences in explicit memory in
(p ¼ .624). the third trimester of pregnancy. Their group
sizes, however, were small (10 pregnant women
and 10 women in the control group). Sharp et al.
DISCUSSION (1993) detected deﬁcits in explicit memory in all
trimesters of pregnancy. Studies performed later
The aim of this study was to investigate whether in pregnancy have yielded conﬂicting data. Casey,
memory and/or information processing speed is Huntsdale, Angus, and Janes (1999), as well as
different in early pregnancy as compared to the McDowall and Moriarty (2000) did not ﬁnd any
nonpregnant state and, if so, which speciﬁc effect of pregnancy on different memory func-
aspects are different. Our results show a clear tions. Brindle et al. (1991) found that implicit
difference between women in early pregnancy memory was signiﬁcantly impaired in primigra-
and their matched controls with regard to perfor- vidae, while explicit memory was unimpaired in
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mance on the WLTtot, its delayed recall, and the contrast to our ﬁndings.
ﬂuency test. These ﬁndings suggest that inten- In our study, speed of information processing
tional learning and retrieval from semantic mem- did not differ between the pregnant women and
ory are compromised. In contrast, speed of the control women. In contrast, Buckwalter et al.
information processing under simple and more (1999) showed a lower performance on tasks
complex conditions was not different. Thus, requiring speed of cognitive processing and
memory functions in particular are affected in conceptual tracking during pregnancy as com-
early pregnancy without consequences for atten- pared with performance after delivery. However,
tion and speed tasks. However, the differences in they administered the tasks late in pregnancy
cognitive performance between the two groups, (19.8 days prior to delivery), in contrast to our
although statistically signiﬁcant, are not large and study, and it may be that these cognitive functions
may not be clinically important. Nevertheless, are only affected later in pregnancy. Thus, in early
there is a possibility that these differences are pregnancy performance on intentional learning
relevant, since they may cause suboptimum tests may be a more sensitive indicator of changed
functioning. Therefore, further research is needed cognitive functioning than performance on speed
to establish the clinical signiﬁcance of the tasks. This is especially since women in the
observed differences. In addition, it should be earlier phases of pregnancy may still have
noted that our study had a cross-sectional design, sufﬁcient attentional ‘resources’ to cope with the
the results of which can be inﬂuenced by selec- demands of speed tasks.
tion-bias. This implies that preexisting perfor- There is uncertainty about the mechanisms
mance differences could have been present underlying the performance deﬁcits seen in
between the groups. Although the careful match- pregnancy. Changes in mood and even depres-
ing between the groups makes it improbable that sion, as well as biological factors, or a combina-
there is a systematic difference between the tion of biological and psychosocial factors have
groups, a longitudinal study is needed in order been mentioned. Concerning the correlation
to rule out this possibility. Till then the results of between mood during pregnancy and cognitive
this cross-sectional study should be interpreted functioning, Harris, Deary, Harris, Lees, and
with caution. Wilson (1996) observed that, after they corrected
As far as we know, there are only few studies, for depression pregnancy was no longer asso-
which investigated cognition in early pregnancy ciated with cognitive dysfunction. However,
MEMORY PERFORMANCE 487
Keenan et al. (1998) found that although pregnant factors, and hormones. A change in LC-PUFA
women scored higher on both depression and availability could, therefore, explain our ﬁndings.
anxiety scales, the pregnancy-related decline in During pregnancy, accretion of maternal, placen-
memory was not attributable to these factors. It is tal and fetal tissue occurs and, consequently, the
not likely that our ﬁndings were inﬂuenced by LC-PUFA requirements of pregnant women and
mood changes or depression, because our study their developing fetuses are high (Clandinin et al.,
was performed in early pregnancy, when mood 1980). To obtain these LC-PUFA, the fetus mainly
changes are minor, if present, in contrast to late depends on placental transfer and thus on the EFA
pregnancy, close to delivery, when a substantial status and/or supply of the mother (Innis, 1991).
proportion of pregnant women experience some- The overall biochemical LC-PUFA status of
times profound psychological changes. However, women declines during pregnancy (Al, van
preexisting mood differences between our two Houwelingen, & Hornstra, 2000) which may have
groups cannot be completely ruled out, as this is functional consequences on maternal cognition.
one of the limitations of a cross-sectional study In summary this cross-sectional study demon-
design as has been stated before. strated less adequate memory performance in an
Several biological factors may underlie the early pregnancy group as compared to a matched
cognitive decline during pregnancy. One factor group of nonpregnant women. A longitudinal
may be hormonal, because the levels of estrogen, study will be needed to establish clear association
progesterone, testosterone, and dehydroepiandos- with pregnancy, especially any causal relation,
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terone change considerably during pregnancy. and to ﬁnd out whether the observed differences
Buckwalter et al. (1999) tried to ﬁnd a relation in early pregnancy disappear at some point after
between impaired memory and the above-men- delivery. Currently, such a study is in progress in
tioned hormones. They conﬁrmed that cognitive our laboratory and results will become available
functioning decreased during pregnancy, especially later this year.
aspects of verbal memory, and that negative mood
states were reported more often during pregnancy
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