Content uploaded by Ilona S Yim
Author content
All content in this area was uploaded by Ilona S Yim
Content may be subject to copyright.
Attenuation of maternal psychophysiological stress responses
and the maternal cortisol awakening response over the course of
human pregnancy
SONJA ENTRINGER1, CLAUDIA BUSS1, ELIZABETH A. SHIRTCLIFF2, ALISON L.
CAMMACK1,3, ILONA S. YIM4, ALEKSANDRA CHICZ-DEMET1, CURT A. SANDMAN1, and
PATHIK D. WADHWA1,5,6
1 Department of Psychiatry and Human Behavior, University of California, Irvine, California, USA
2 Department of Psychology, University of New Orleans, Irvine, Los Angeles, USA
3 School of Public Health, Emory University, Atlanta, Georgia, USA
4 Department of Psychology and Social Behavior, University of California, Irvine, California, USA
5 Department of Obstetrics and Gynecology, University of California, Irvine, California, USA
6 Department of Pediatrics, University of California, Irvine, California, USA
Abstract
The effects of maternal stress during pregnancy may depend, in part, on the timing in gestation of
the occurrence of stress. The aim of the present study was to examine the effect of stage of gestation
on maternal psychophysiological responses to stress using a standardized laboratory paradigm and
on the cortisol response to awakening (CAR). A longitudinal design was employed to quantify
maternal psychophysiological stress reactivity [changes in heart rate (HR), blood pressure, salivary
cortisol, and psychological distress in response to the trier social stress test (TSST)] and the CAR at
approximately 17 and 31 weeks gestation in a sample of 148 women. To account for the possible
effects of habituation when being exposed to the same stress protocol twice, a non-pregnant
comparison group (CG, N = 36) also underwent these assessments at two time points, with a
comparable time interval between the assessments. In both groups, the TSST elicited significant
changes in maternal HR, mean arterial pressure, and psychological distress levels but not a significant
increase in cortisol levels. Among the pregnant women (pregnant group(PG)), the stressor-induced
increases in HR, blood pressure, and psychological distress were significantly lower at the second
(31 weeks gestation) compared to the first (17 weeks gestation) assessment of pregnancy (all p <
0.01). The maternal CAR was also significantly attenuated in later compared to earlier gestation (p
= 0.003). In the CG, there were no significant differences in psychophysiological stress responses
and in the CAR across the two assessments. Among pregnant women there is a progressive
attenuation of psychophysiological stress responses with advancing gestation. This attenuation is
unlikely to be attributable to habituation. Individual differences in the degree of attenuation of stress
responses over gestation may represent a novel marker of stress susceptibility in human pregnancy.
Correspondence: P. D. Wadhwa, Behavioral Perinatology Research Program, Department of Psychiatry and Human Behavior, University
of California, 3117 Gillespie Neuroscience Research Facility, Irvine, CA 92697, USA. Tel: 949 824 8238. Fax: 949 824 8218.
pwadhwa@uci.edu.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the
paper.
NIH Public Access
Author Manuscript
Stress. Author manuscript; available in PMC 2010 May 3.
Published in final edited form as:
Stress. 2010 May ; 13(3): 258–268. doi:10.3109/10253890903349501.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Keywords
Cortisol awakening response (CAR) or rise; heart rate; mean arterial pressure; pregnancy;
psychosocial stress; Trier Social Stress Test (TSST)
Introduction
Exposure to high levels of maternal stress during pregnancy has the potential to adversely
impact fetal development, birth outcomes, and subsequent child and adult health outcomes
(Van den Bergh et al. 2005; Wadhwa 2005; Entringer et al. 2008; Weinstock 2008; O’Donnell
et al. 2009). There is, however, considerable variation in the effects of prenatal stress (Wadhwa
2005). One possible modifier of its effects is timing of the occurrence of stress. There may be
critical time periods in human gestation of increased susceptibility to the effects of maternal
stress. The notion of critical periods of susceptibility has been discussed previously, and its
effects are usually attributed to the underlying ontogeny or time line of the development of the
fetal brain and other organ systems (Rice and Barone 2000; Nijland et al. 2008), to suggest
that a system may be most vulnerable to the effects of stress during its most rapid phase or
phases of growth and development. We propose here another potential explanation for this
phenomenon: as pregnancy advances there are progressive changes in maternal biology which,
in turn, may result in alterations in physiological and psychological responses to stress and
thereby produce variation in the effects of prenatal stress on the developing fetus.
It is well established that the state of pregnancy produces major alterations in physiological
systems, including up-regulation of hormone production and cardiac output, that are crucial
for supporting aspects of fetal growth and development (see Mastorakos and Ilias 2003 for an
overview). Some evidence suggests that the state of pregnancy is associated with alterations
in maternal physiological responsivity to a stimulus or stressor. Evoked physiological
(cardiovascular and endocrine) responses have been studied in pregnant women in response to
pharmacological and physical challenges. These studies generally suggest that maternal
responses to challenge are dampened in pregnancy, particularly in the latter stages of gestation.
For example, administration of exogenous corticotrophin-releasing hormone (CRH) in late
pregnancy failed to evoke a significant pituitary or adrenal response (Sasaki et al. 1989; Schulte
et al. 1990), and administration of dexamethasone produced less suppression of cortisol
production (Odagiri et al. 1988). Similarly, autonomic responses [heart rate (HR), blood
pressure] to a variety of challenges, including exercise, orthostatic challenge, and the cold
pressure test, are attenuated in pregnancy (Ekholm and Erkkola 1996; Wolfe and Weissgerber
2003; de Weerth et al. 2005). Much less research, however, has been conducted regarding
maternal responsivity to psychological stress during pregnancy. Studies in pregnant women
that have employed laboratory-based challenge paradigms to induce psychological stress (e.g.
cognitive challenge tests such as mental arithmetic, Stroop test, free speech, and mirror image
tracing) are reviewed in deWeerth et al. (2005). The results of these studies generally suggest
that blood pressure, HR, and cortisol responses to psychological stress appear to be attenuated
in pregnancy. Two recent studies did not find differences in cortisol and HR responses to a
laboratory stress protocol between pregnant and non-pregnant women (Nierop et al. 2006a;
de Weerth et al. 2007). However, differences in experimental designs, the lack of adequate
control groups, and other methodological limitations make it difficult to draw firm conclusions.
Moreover, it is possible that the psychological appraisal of a stressful stimulus/experience also
may be altered during pregnancy: some studies have suggested that women seem to become
decreasingly sensitive to the psychological effects of stress as pregnancy advances (Glynn et
al. 2001, 2004, 2008).
ENTRINGER et al. Page 2
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Thus, the aim of the present study was to systematically investigate whether there are changes
over the course of human gestation in sympathoadrenal medullary (SAM), hypothalamic–
pituitary–adrenal (HPA), and psychological responses to psychosocial stress. A prospective,
longitudinal design with serial assessments was employed to assess maternal
psychophysiological reactivity (HR, blood pressure, cortisol, and psychological appraisal of
distress) in response to a standardized laboratory-based psychosocial stressor—the Trier Social
Stress Test (TSST)—at two time points in the second and third trimester of pregnancy,
respectively. The TSST was selected because it combines two critical elements of the
experience of psychosocial stress—uncontrollability and social-evaluative threat—and has
been shown in many different populations to reliably induce psychophysiological stress
responses (Dickerson and Kemeny 2004). We also simultaneously assessed the maternal
cortisol awakening response (CAR)—the rise in cortisol secretion following transition from
sleep to wake in the morning. In addition, circadian regulation of cortisol production was
assessed using the short diurnal cortisol profile. To control and distinguish the potential effects
of habituation (Kirschbaum et al. 1995; Federenko et al. 2004) from those of pregnancy-related
attenuation, a non-pregnant comparison group (CG) underwent the same protocol at two time
points with a comparable time interval between assessments. We hypothesized (1) that the
cardiovascular, endocrine, and psychological responses to the TSST as well as the CAR would
be progressively attenuated as pregnancy advanced, and (2) that the magnitude of this
attenuation would be greater than that of a possible habituation effect (as measured in the non-
pregnant CG).
Materials and methods
Participants
A total of 148 pregnant women (PG) receiving prenatal care at university-affiliated obstetric
clinics in Southern California were recruited as subjects for this study. Inclusion criteria were
a singleton, intrauterine pregnancy < 20 weeks gestation. Exclusion criteria included tobacco,
alcohol, or other drug use in pregnancy; uterine or cervical abnormalities; or presence of any
conditions known to be associated with dysregulated cardiovascular or neuroendocrine
function, such as endocrine, hepatic, or renal disorders or corticosteroid medication use. The
mean age was 28.54 ± 0.49 (SEM) years; approximately half of the sample were nulliparous
women (46.3%) of predominantly non-Hispanic White (39.2%), and Hispanic (30.7%) origin
(see Table I).
For all subjects gestational age was determined by best obstetric estimate with a combination
of last menstrual period and early uterine size, and was confirmed by obstetric ultrasonographic
biometry using standard clinical criteria (O’Brien et al. 1981). The sample was predominantly
low obstetric risk for adverse pregnancy outcomes; obstetric risk was abstracted from the
medical record and coded as a dichotomous variable as previously described (Wadhwa et al.
2004).
A non-pregnant CG of women was recruited by presenting the study to university employees
through e-mail announcements and placards. Exclusion criteria for the CG were smoking or
presence of any conditions known to be associated with dysregulated cardiovascular or
neuroendocrine function, such as endocrine, hepatic or renal disorders, or corticosteroid
medication use. As presented in Table I, the CG was significantly older, but there were no
significant differences regarding race/ethnicity, education, marital status, body mass index
(BMI), and parity between the PG and the CG. All 36 CG women completed the first
assessment, and 22 subjects completed both assessments. The CG women who had dropped
from the study after the first assessment did not differ significantly from the CG women who
completed both assessments. The study was approved by the Institutional Review Board and
all study participants provided written informed consent.
ENTRINGER et al. Page 3
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Experimental procedures
Subjects reported to the research laboratory on two occasions. Of the 148 pregnant women,
118 subjects provided complete data at the first assessment during pregnancy [16.6 ± 0.14
(SEM) weeks gestation], 106 subjects provided complete data at the second assessment (31.5
± 0.12 weeks gestation), and 76 subjects completed both visits†. Subjects that completed both
visits did not differ at recruitment from subjects that only completed one of the two visits with
respect to age, parity, race/ethnicity, levels of perceived stress (assessed using the Perceived
Stress Scale, Cohen et al. 1983) and depressive symptoms (assessed using the Center for
Epidemiological Studies Depression Scale, Radloff 1977; all p > 0.14). The mean time between
the first and second assessments was 14.4 ± 0.19 weeks. These two time periods, around 17
and 30 weeks gestation, were selected because the change in endocrine parameters from early
through late gestation is critical in characterizing the maternal–placental–fetal endocrine stress
milieu with respect to its impact on parturition (Hobel et al. 1999;Wadhwa et al. 2001;Sandman
et al. 2006). The CG of non-pregnant subjects also attended two laboratory sessions at a
comparable time interval (15.8 ± 0.3 weeks). The time interval between the two sessions did
not differ significantly between the PG and the CG.
All participants were instructed to refrain from physical exercise and non-prescription
medication (e.g. antihistamines, antiinflammatory medications) 24 h prior to the assessment,
refrain from caffeine intake in the preceding 4 h period, and only consume a light carbohydrate
lunch on the day of the assessment, at least 60 min before the assessment. Each participant was
exposed to the psychosocial stress protocol (TSST) in the afternoon at identical times across
test days, commencing between 1430 and 1600 h. Time of day was controlled to avoid baseline
level or reactivity differences due to the circadian rhythm of HPA axis activity.
Thirty minutes prior to the onset of the TSST, subjects were seated in a comfortable armchair
in a recumbent position and were instrumented with Dinamap vital signs monitors (1846 SX,
Critikon) for automated assessment of HR and blood pressure. Participants remained seated in
this position and in the same room during the whole procedure. This was a modification to the
standard TSST protocol (Kirschbaum et al. 1993) to minimize physical discomfort to the
pregnant women. After a 30 min relaxation period, participants were exposed to the TSST,
which consists of a free speech (5 min) and a mental arithmetic task (5 min) in front of an
audience and a camera. Including the instruction and a short preparation period, the stressful
situation lasted for 15 min. HR and blood pressure were assessed −30, −15, and −1 min prior
to, as well as every +3 min up to +30 min after the onset of the TSST. Saliva samples were
collected −15 and −1 min prior to and at +16, +30, +45, and + 60 min relative to the onset of
the TSST.
To assess diurnal cortisol profiles, subjects were instructed to collect saliva samples at 0, 30,
45, and 60 min after awakening as well as at 1200, 1500, and 2000 h on the day before the
TSST exposure. Exact time of saliva sampling was monitored using a Medication Event
Monitoring System (MEMS®, Aardex group, Union City, CA, USA) that time stamped every
opening of the plastic vial where the swabs to collect the saliva were stored. The use of an
electronic monitoring device has been shown to increase compliance regarding the exact time
of the sample collection, which, in turn, is critical for accurately characterizing an individual’s
circadian profile (Kudielka et al. 2003). Accordingly, each swab was stored in a plastic tube
labeled with the designated sampling time by the experimenter. Participants were instructed
to refrain from brushing their teeth during the first hour after awakening and from eating 30
min before each saliva collection.
†Our final models included all 148 subjects. However, analyses on only the subgroup of subjects that completed both visits (n = 76)
provided similar results (significant effects with comparable effect sizes), albeit with reduced statistical power.
ENTRINGER et al. Page 4
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Psychological stress assessments
To obtain a measure of perceived distress associated with the task, participants were asked to
rate how distressed they felt immediately before and after the task on a 5-point Likert scale
ranging from 0 (not at all) to 4 (“extremely”, adapted from the “profile of mood states”, McNair
et al. 1981).
Salivary cortisol assay
Saliva samples were collected using a Salivette sampling device (Sarstedt, Numbrecht,
Germany). Saliva was recovered from each swab by centrifugation and stored at −70°C degrees
until assayed. Thawed samples were centrifuged at 1700g for 15 min before assay. Salivary
cortisol concentrations were determined by a competitive luminescence immunoassay (LIA;
IBL-America, Minneapolis, MN, USA) with a detection limit of 0.015 μg/dl. The cross
reactivity of the assay was < 2.5% with cortisone, prednisone, and corticosterone and < 0.1%
with other naturally occurring steroids. The intra- and inter-assay coefficients of variance were
5.5 and 7.6%, respectively. Data reduction for the LIA assay was done by an automated four-
parameter logistics program (software Mikro Win 2000; Berthold Microplate Luminometer).
All samples were assayed in duplicate and averaged.
Statistical analyses
Hierarchical linear modeling (HLM) growth curve analyses (Raudenbush and Bryk 2002;
Singer and Willett 2003) were conducted using the HLM 6.01 for Windows software package
to characterize changes in HR, blood pressure, and cortisol concentrations in response to the
TSST as well as cortisol responses to awakening and changes over the course of the day. The
HLM procedure weights cases with complete data more heavily, but all cases are included in
the estimation of effects. We used precise measures of time of day for sample collection (i.e.,
actual times of collection recorded by the MEMS® cap) and gestational age at testing rather
than nominal estimates of assessment intervals in order to control for variability in the timing
of collections or stage of pregnancy. All analyses were performed separately for pregnant
women and the CG in order to control for pregnancy-related covariates among the pregnant
group. All cortisol measures were log transformed by LnCort = ln (Cort + 1) to yield an
unskewed response variable. Because mean arterial pressure (MAP) is a better predictor of
pregnancy complications than either systolic or diastolic blood pressure (Cnossen et al.
2008), MAP was used and was calculated by the following formula: [(2 × diastolic) + systolic]/
3 (diastole is weighted 2 × systole because 2/3 of the cardiac cycle is spent in diastole). The
statistical significance level was set at alpha = 0.05.
Analyses of HR, MAP, and cortisol levels in response to the TSST over gestation
The assessments prior to the start of the TSST were averaged to obtain a baseline measure. As
depicted in Figure 1, subjects, on average, returned to their baseline HR and MAP levels 21
min after the start of the TSST. The time interval from baseline until 21 min after the onset of
the TSST was therefore considered the response period.
Three-level HLM analyses were performed to evaluate stage-of-gestation related changes in
maternal HR and MAP in response to the TSST. Level 1 captured parameters that change within
an individual and within an assessment period i.e., time as random predictors of HR, MAP,
and cortisol, respectively. Linear and quadratic effects of time were included in the final model,
and comparison of deviance statistics showed that this model was superior to linear modeling
(all p < 0.001). Time was centered at baseline so that the intercept represented the mean HR,
MAP, or cortisol levels just prior to the start of the TSST.
ENTRINGER et al. Page 5
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Level 2 captured potential changes in stress physiology from one assessment to the next. For
pregnant women, exact gestational age at testing (in weeks gestation) at each assessment was
modeled (centered at mean gestational age at first visit) to capture change in stress physiology
across pregnancy. For CG subjects, the first visit was set to zero to parallel the model for the
pregnant women, and time in weeks captured the interval between visits.
Between individual differences predictors were introduced in level 3. Covariates of interest
included age and BMI (pre-pregnancy BMI for the pregnant group) for both groups, and
obstetric risk and fetal sex for the pregnant group. None of these variables influenced the
changes in HR over gestation. There was, however, a significant effect of fetal sex on changes
in maternal MAP responses to the TSST over gestation (p = 0.025). Hence, the results presented
below are adjusted for the effects of fetal sex.
Analysis of psychological distress over pregnancy
Differences in distress levels from before to after the TSST at each assessment were calculated
for each individual (Δ distress). Two-level models were constructed to model changes in Δ
distress in response to the TSST over gestation (from first to second for the CG, respectively).
Analyses of diurnal cortisol over gestation
Three-level HLM models were performed to evaluate possible gestational-age related changes
in the diurnal cortisol profile over pregnancy. Because the CAR (assessed at 0, 30, 45, and 60
min after awakening) and the slope over the day (day time profile, assessed at awakening, 1100,
1600, and 2000 h) are considered two different characteristics of HPA axis function (Pruessner
et al. 1997; Wust et al. 2000; Wilhelm et al. 2007), level 1 included two time parameters, one
for the CAR effect, and the second parameter for the short daytime profile to capture within-
the-day changes in cortisol. Both the CAR and the diurnal slope were simultaneously modeled
to account for the potential interdependence of these parameters and to ensure that associations
with gestational age or individual differences were independently associated with cortisol
levels, the CAR, and/or the diurnal slope. Based on known changes in the awakening and
daytime pattern of cortisol production, linear and quadratic effects of time for both parameters
were included, and this proved to be superior to linear modeling (all p < 0.001). Time was
centered at awakening so that model intercept represents the mean log transformed cortisol
levels at awakening. The two time parameters and the intercept were included as random factors
since they are known to have substantial variability across individuals.
Exact gestational age at each assessment for the pregnant women (centered at mean gestational
age at first visit) and time between visits for the CG were modeled at level 2. Not all participants
awoke at the same time at each assessment period. To control for fluctuations in wake up time
at each assessment, time of awakening was entered at level 2.
Level 3 captured between individual differences in predictors. Covariates of interest included
maternal age, obstetric risk, pre-pregnancy BMI, and fetal sex. None of these variables
influenced the change in cortisol concentrations and were therefore not included in the final
models (all p > 0.15).
In order to examine the relative magnitude of the HR, MAP, and distress response attenuation
across gestation in the pregnant women (and across time in the CG), we calculated the R2, the
percent of session-by-session variance explained by gestational age (or time). The percentage
of variance explained in an HLM model is complicated because variance at each different level
of analyses can individually change with the inclusion of a predictor (Hox 2002). Consequently,
for our purposes, the interpretation of the R2 described by Hox (2002) and Snidjers and Bosker
(1994) is specific to the session-by-session level of analysis.
ENTRINGER et al. Page 6
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Results
Physiological and psychological responses to the TSST
The mean values (±SEM) of HR and MAP for pregnant women and the non-pregnant CG
before, during, and after the TSST at both visits are depicted in Figure 1.
Heart rate
Table IIa shows results of the three-level HLM model for HR for pregnant women. Baseline
HR was significantly higher in the later compared to earlier stage of pregnancy (p < 0.001).
Basal HR increased by 0.52 beats per minute with each week of advancing gestation. The HR
increase in response to the TSST was less steep as gestation advanced (p < 0.001) indicated
by the significant stage of gestation-related changes in the linear and quadratic time slopes (all
p < 0.001).
In contrast, the HR increase in response to the TSST in the CG was not different from the first
to the second assessment, as indicated by no effect of weeks between visits on the intercept
and the linear and quadratic slopes, all p > 0.88.
Mean arterial pressure
Table IIb shows the results of the three-level HLM model for MAP for pregnant women. There
were no differences in baseline MAP across the two assessments in earlier and later gestation
(p = 0.239). The increase in MAP in response to the TSST was, however, less steep as gestation
advanced (p’s for interaction between linear and quadratic slopes and week of gestation <
0.005)‡.
In the CG, MAP responses to the TSST were not different across the two assessments (no
significant effect of weeks between visits on the intercept, the linear slope or the overall shape
of the curve, all p > 0.101).
Salivary cortisol concentration
In this population of subjects using the procedures described above, exposure to the TSST did
not produce a significant increase in salivary cortisol concentration at either of the two
assessments in either the pregnant and non-pregnant group (for linear slope, all p > 0.07). We,
therefore, did not conduct any further HLM models to examine changes in the salivary cortisol
response to the TSST across the two assessments.
Psychological distress
As expected, exposure to the TSST induced significant psychological distress in subjects in
both groups. Among pregnant women, the extent of psychological distress evoked by the TSST
was significantly attenuated as gestation advanced (B = −0.0348, SE = 0.0088, and p < 0.001,
see Figure 2), whereas it did not differ in the CG across the two assessments (B = −0.0248, SE
= 0.0144, and p = 0.092).
Table III shows the percent of session-by-session variance explained by gestational age for the
PG or time between sessions for the CG (R2). The proportion of variance in changes in the
response magnitude from TSST1 to 2 explained by the state of pregnancy is higher (47% for
HR, 10% for MAP, and 19% for distress) than the session-by-session variance explained by
habituation to the task in the CG (0% for HR, 5% for MAP, and 4% for distress) indicating
‡Running the same models for systolic and diastolic blood pressure separately yielded similar results.
ENTRINGER et al. Page 7
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
that the attenuation effect we observed in the PG is over and above the effect explained by
habituation to the task in the CG.
Diurnal cortisol concentrations over the course of gestation
Mean cortisol concentrations (±SEM) in response to awakening and over the course of the day
are presented for both study groups in Figure 3. The results of the final three-level HLM model
on log-transformed salivary cortisol for pregnant women are summarized in Table IV. The
main effects “Time” for CAR and course of day reflect changes in cortisol concentrations after
awakening and over the course of the day, respectively. As indicated by the significant linear
and quadratic time slope for the CAR (all p < 0.001), a significant increase in cortisol
concentrations was observed in the first hour after awakening, and there was also a quadratic
effect, as illustrated in Figure 3. Furthermore, from awakening to 20:00 h, cortisol
concentrations decreased significantly reflected by the linear day time slope (p < 0.001). These
results suggest that during pregnancy, the diurnal cortisol rhythmicity (increase in response to
awakening and a general decrease over the course of the day) is preserved.
The cross-level interactions between “Time” (CAR and day) and week of gestation (earlier vs.
later in pregnancy) indicate how diurnal cortisol concentrations changed over the course of
gestation. As expected, cortisol concentrations at awakening (intercept) significantly increased
with gestational age (p < 0.001). The cortisol increase in response to awakening was, however,
less steep and more platykurtic as gestation advanced indicated by significant gestation-related
changes in the linear and quadratic CAR time slopes (all p ≤ 0.001).
The diurnal cortisol rhythm over the course of the day did not change significantly as gestation
advances (as reflected by the linear day time slope (p = 0.07). Thus, the results suggest that
after accounting for the changing baseline across gestation, there is a significantly smaller CAR
with advancing gestation.
The CG also showed a significant cortisol increase in response to awakening as well as a
decrease in cortisol concentrations over the course of the day at both assessments (for quadratic
and linear CAR and day slopes, all p < 0.001). However, there were no significant changes
across the two assessments in the magnitude of the CAR or the diurnal cortisol rhythm (no
effect of weeks between visits on the intercept and the linear and quadratic time slopes, all p
> 0.90).
Discussion
To the best of our knowledge, this is the first study to prospectively and longitudinally assess
serial psychophysiological responses to a standardized laboratory-based psychosocial stress
test as well as the CAR in pregnant women over the course of gestation and in a non-pregnant
CG. As expected, baseline salivary cortisol and HR levels were significantly higher in the third
compared to the second trimester of gestation. However, the CAR, as well as the increase in
HR and MAP in response to the TSST were attenuated in the later compared to earlier stage
of pregnancy. Moreover, the TSST-induced levels of psychological distress were also lower
in later compared to earlier gestation. Thus, the findings of the present study not only replicate
earlier reports suggesting physiological responses to challenge are dampened during
pregnancy, but also suggest that there is a progressive attenuation of maternal physiological
as well as psychological stress responses with advancing gestation. Because the non-pregnant
CG did not exhibit significant differences in any of these parameters across the two
assessments, we believe it is unlikely that the progressive attenuation of the stress responses
in pregnant women is due to habituation to the task.
ENTRINGER et al. Page 8
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Although baseline levels increase over gestation (which is expected because pregnancy is
associated with a progressive increase in hormone production), and although the law of initial
values would postulate that the predicted decrease in response to a challenge is a function of
the elevated baseline, our results suggest that even after accounting for baseline (which is done
in the HLM model by examining level and change simultaneously, thereby partialing out the
effects of one from the other at the appropriate level of analysis), the response to challenge
(TSST, awakening) is attenuated with advancing gestation. Thus, because the observed
attenuation of stress response is independent of baseline function, future studies in this cohort
could examine whether individual differences in the degree of attenuation across gestation may
serve as a marker of underlying susceptibility for prenatal stress-related outcomes in the
offspring.
Our findings are consistent with those of Matthews and Rodin (1992), who reported that
pregnancy was associated with a reduced diastolic blood pressure response across a variety of
different stress tasks, and with those of DiPietro et al. (2003), who noted a decline in the
maternal HR response to a psychological stressor from 24 to 36 weeks gestation. The use of
the TSST, a standardized protocol to induce psychosocial stress, has so far been reported only
twice in the context of human pregnancy (Nierop et al. 2006a,b; de Weerth et al. 2007). In
contrast to our repeated measures longitudinal design, Nierop et al. (2006a) used a cross-
sectional study design and did not observe any differences in HR response to the TSST in
second compared to third trimester-pregnant women. They did, however, report smaller alpha-
amylase responses to the TSST in third versus second trimester pregnant women. The activity
of this enzyme in saliva is believed to reflect SAM reactivity (Ehlert et al. 2006); hence this
aspect of their findings is consistent with our finding of a progressively attenuated
cardiovascular response from mid to later pregnancy. Our findings of lower distress in response
to the TSST over the course of gestation are consistent with previous reports suggesting a
decline in perceived stress, state anxiety, and affective responses to specific life events during
pregnancy (Glynn et al. 2001, 2004, 2008).
We are aware of two other studies examining the CAR in the context of pregnancy (de Weerth
et al. 2007; Shea et al. 2007). Although Shea et al. (2007) reported an increase of about 44%
from awakening to 30 min after awakening in their healthy pregnant group, they also state at
the same time that the absolute increase of 5.3 nmol/l is much lower than the 9 nmol/l cortisol
increase to awakening reported in healthy non-preganant women (Clow et al. 2004), which is
in line with our findings. In addition, we note that they assessed the CAR on average at 28
weeks gestation, while in the present study the late pregnancy visits took place on average
about 3 weeks later, at 31 weeks gestation. This could explain why the baseline awakening
levels we observed at the second visit were on average higher than those reported by Shea et
al. (2007), because cortisol levels increase progressively over gestation reaching levels 2–3
times as high at the end of pregnancy compared to non-pregnant women. In the de Weerth and
Buitelaar study (2005), the CAR was assessed during pregnancy and 9 months postpartum in
the same women. They report that the relative mean increase was comparable at both time
points. As the authors point up in their discussion, the awakening response of mothers of 9-
month-old-infants might be influenced by interruptions of sleep, and the women may not have
been as compliant with the sampling protocol during motherhood. In addition, there are
methodological differences regarding the sampling protocol and statistical analyses between
our study and the two above-mentioned studies. Since it has been suggested that compliance
and the accuracy of self-reported sampling records increases when participants are informed
that an electronic monitoring device is recording their saliva collection activities (Kudielka et
al. 2003), electronic monitoring devices (MEMS®, AAR-DEX) were used to time and date
stamp instances of saliva collection, and exact time of sampling was used in the statistical
models, while the de Weerth et al. (2005) and Shea et al. (2007) studies relied on self-reported
sampling time.
ENTRINGER et al. Page 9
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
A recent review of physiological stress reactivity in pregnancy by de Weerth and Buitelaar
(2005) highlights several major methodological limitations in the existing literature and makes
recommendations for future research. We note that our study design incorporated almost all
of these recommendations i.e., investigating stress reactivity throughout pregnancy using a
longitudinal design, and the inclusion of a non-pregnant CG. There are, however, some
limitations to our study. Although the psychosocial stress protocol used by us (the TSST)
successfully stimulated the SAM system at all assessments (as indicated by significant
increases in HR and blood pressure), we did not observe a significant endocrine (cortisol)
response to the task. We speculate that the failure of the task to produce a significant cortisol
response in not only the pregnant but also the non-pregnant women may be a consequence of
our modification of the standard TSST protocol. Because we used the stress protocol twice
during pregnancy (second and third trimester), we tried to find a balance between choosing a
stressor that was potent enough to reliably elicit a stress response, but that did not induce any
physical discomfort in the third trimester pregnant women. Our modification of the TSST had
the subjects comfortably seated in the same room during the anticipation, stress, and recovery
periods, and we speculate this may have decreased the novelty, uncertainty, and
unpredictability of the situation, which are important situational factors for stress activation
(Mason 1968; Dickerson and Kemeny 2004). In addition to those factors, the degree of social
evaluative threat experienced in a stressful situation seems to be an important factor in eliciting
a cortisol response (Gruenewald 2004; Dickerson 2008). Gruenwald et al. (2004) reported that
not all physiological systems are activated in parallel or at the same threshold by a
psychological stressor. In their experiment, they manipulated the degree of social evaluative
threat that the subjects were exposed to during a speech and mental arithmetic stress task (two
conditions: high and low evaluative threat). In the low social evaluative threat condition,
participants did not mount a significant cortisol response, while HR and BP showed large
increases in both conditions, and Dickerson et al. (2008) reported similar findings. The fact
that the subjects were reclined in an armchair in front of the jury may have made the situation
more informal and familiar, and therefore may have reduced the experience of social evaluative
threat. This may explain while we did not observe a cortisol response, while the task was still
potent enough to stimulate the SAM system and evoke a feeling of distress at all assessments.
The sample size of our CG was smaller than the sample size of the pregnant group. However,
we do not believe that the fact that the attenuation of the response magnitude of HR, MAP and
distress was significant in the PG and non-significant in CG was due to lack of statistical power
in the CG, since the percent of session-by-session variance explained by gestational age (R2)
is much larger than the percent of session-by-session variance explained by time between
sessions for the CG. Direct comparison of the pregnant versus control participants in a single
statistical model was not possible given our pregnancy specific covariates, so one limitation is
that the comparison is primarily descriptive. Addressing this limitation in future work will be
important, yet difficult because pregnancy represents a unique physiological state of a woman’s
life.
Changes in neuroendocrine function during human pregnancy include a progressive increase
in placental CRH and maternal adenocrticotropic hormone (ACTH) and cortisol levels over
the course of gestation. A consequence of the increase in baseline levels may be downregulation
of receptor sensitivity and therefore reduced responsiveness of the system to challenge. One
implication of our findings of attenuated physiological as well as psychological responsivity
to stress with advancing gestation supports the importance of the timing of the occurrence of
stress during pregnancy in terms of its potentially detrimental effects. Thus, the effects of stress
on the developing fetus may be more detrimental earlier than later in pregnancy. In addition,
the activity of the placental enzyme, 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2),
which oxidizes cortisol to its inactive form cortisone, increases during pregnancy, thereby
resulting in a reduction of the proportion of maternal cortisol passing into the fetal compartment
ENTRINGER et al. Page 10
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
(Murphy et al. 2006). The moderating effect of timing of stress in pregnancy also may depend,
as discussed earlier, on the ontogeny of fetal development. Systems may be most vulnerable
to the effects of maternal stress when undergoing rapid development suggesting that systems
that develop earlier in gestation may be more vulnerable to the effects of maternal stress. For
these reasons, it is possible that individual differences in the degree of dampening of stress
responses over the course of gestation may represent a marker of stress susceptibility.
What drives these changes in maternal responses to stress over gestation and hence potentially
alters its putative effects on the developing fetus? An implicit assumption regarding the
direction of causality is that it is unidirectional in nature, in that potentially unfavorable
circumstances in a pregnant woman’s life that are perceived or appraised by the maternal brain
as stressful may then influence maternal physiology, which, in turn, may impact the developing
embryo/fetus via direct or indirect biological mechanisms, as discussed above. However, the
alterations in maternal physiology associated with pregnancy are known to originate from the
fetal compartment (the placenta is an organ of fetal origin). Because these observed variations
in maternal physiology (that have consequences for maternal stress responses and fetal
susceptibility to maternal stress exposure) originate in and are sustained by the developing
fetus over gestation, there is the intriguing possibility of reciprocal, bidirectional causality, in
which variations in processes that underlie fetal growth, maturation, and development result
in variations in maternal physiology which, in turn, influence or moderate the effects of
maternal stress exposure on the developing fetus, including perhaps, subsequent changes in
maternal physiology and fetal susceptibility to maternal stress. The object (fetus) of the
influence (effects of maternal stress) is the cause of the process that produces the influence
(changes in maternal stress responsivity); this process is dynamic, recursive, and bidirectional
between the fetal and maternal compartment over the course of gestation.
Taken together, the findings of the present study establish that maternal responsivity to stress
is attenuated as pregnancy advances and thereby suggest that the timing of the occurrence of
stress in pregnancy may matter in terms of its potential impact on fetal development and
subsequent health outcomes. More empirical research is needed to examine the role of
individual differences in the degree of attenuation as a marker of underlying fetal
pathophysiology, in terms of its effects on pregnancy, fetal development, and subsequent birth,
child, and adult health outcomes.
Acknowledgments
This study was supported, in part, by US PHS (NIH) grants HD-33506, HD-041696, and HD-47609 to PDW.
References
Clow A, Thorn L, Evans P, Hucklebridge F. The awakening cortisol response: Methodological issues
and significance. Stress 2004;7:29–37. [PubMed: 15204030]
Cnossen JS, Vollebregt KC, de Vrieze N, ter Riet G, Mol BW, Franx A, Khan KS, vam der Post JA.
Accuracy of mean arterial pressure and blood pressure measurements in predicting pre-eclampsia:
Systematic review and meta-analysis. BMJ 2008;336:1117–1120. [PubMed: 18480117]
Cohen S, Kamarck T, Mermelstein R. A global measure of perceived stress. J Health Soc Behav
1983;24:385–396. [PubMed: 6668417]
de Weerth C, Buitelaar JK. Physiological stress reactivity in human pregnancy–A review. Neurosci Bio
behav Rev 2005;29:295–312.
de Weerth C, Wied CC, Jansen LM, Buitelaar JK. Cardiovascular and cortisol responses to a
psychological stressor during pregnancy. Acta Obstet Gynecol Scand 2007:1–12. [PubMed:
17851798]
DiPietro JA, Costigan KA, Gurewitsch ED. Fetal response to induced maternal stress. Early Hum Dev
2003;74:125–138. [PubMed: 14580752]
ENTRINGER et al. Page 11
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Dickerson SS, Kemeny ME. Acute stressors and cortisol responses: A theoretical integration and
synthesis of laboratory research. Psychol Bull 2004;130:355–391. [PubMed: 15122924]
Dickerson SS, Mycek PJ, Zaldivar F. Negative social evaluation, but not mere social presence, elicits
cortisol responses to a laboratory stressor task. Health Psychol 2008;27(1):116–21. [PubMed:
18230022]
Ehlert U, Erni K, Hebisch G, Nater U. Salivary alpha-amylase levels after yohimbine challenge in healthy
men. J Clin Endocrinol Metab 2006;91:5130–5133. [PubMed: 16968802]
Ekholm EM, Erkkola RU. Autonomic cardiovascular control in pregnancy. Eur J Obstet Gynecol Reprod
Biol 1996;64:29–36. [PubMed: 8801145]
Entringer S, Wust S, Kumsta R, Layes IM, Nelson EL, Hellhammer DH, Wadhwa PD. Prenatal
psychosocial stress exposure is associated with insulin resistance in young adults. Am J Obstet
Gynecol 2008;199:498, e491–e497. [PubMed: 18448080]
Federenko IS, Nagamine M, Hellhammer DH, Wadhwa PD, Wust S. The heritability of hypothalamus
pituitary adrenal axis responses to psychosocial stress is context dependent. J Clin Endocrinol Metab
2004;89:6244–6250. [PubMed: 15579784]
Glynn LM, Wadhwa PD, Dunkel-Schetter C, Chicz-Demet A, Sandman CA. When stress happens
matters: Effects of earthquake timing on stress responsivity in pregnancy. Am J Obstet Gynecol
2001;184:637–642. [PubMed: 11262465]
Glynn LM, Schetter CD, Wadhwa PD, Sandman CA. Pregnancy affects appraisal of negative life events.
J Psychosom Res 2004;56:47–52. [PubMed: 14987963]
Glynn LM, Schetter CD, Hobel CJ, Sandman CA. Pattern of perceived stress and anxiety in pregnancy
predicts preterm birth. Health Psychol 2008;27:43–51. [PubMed: 18230013]
Gruenewald TL, Kemeny ME, Aziz N, Fahey JL. Acute threat to the social self: Shame, social self-
esteem, and cortisol activity. Psychosom Med 2004;66(6):915–24. [PubMed: 15564358]
Hobel CJ, Dunkel-Schetter C, Roesch SC, Castro LC, Arora CP. Maternal plasma corticotropin-releasing
hormone associated with stress at 20 weeks’ gestation in pregnancies ending in preterm delivery. Am
J Obstet Gynecol 1999;180:S257–S263. [PubMed: 9914629]
Hox, JJ. Multilevel analyses: Techniques and applications. Mahwah, New Jersey: Lawrence Erlbaum
Associates; 2002.
Kirschbaum C, Pirke KM, Hellhammer DH. The “trier social stress test”–A tool for investigating
psychobiological stress responses in a laboratory setting. Neuropsychobiology 1993;28:76–81.
[PubMed: 8255414]
Kirschbaum C, Prussner JC, Stone AA, FederenkoI, Gaab J, Lintz D, Schommer N, Hellhammer DH.
Persistent high cortisol responses to repeated psychological stress in a subpopulation of healthy men.
Psychosom Med 1995;57:468–474. [PubMed: 8552738]
Kudielka BM, Broderick JE, Kirschbaum C. Compliance with saliva sampling protocols: Electronic
monitoring reveals invalid cortisol daytime profiles in noncompliant subjects. Psychosom Med
2003;65:313–319. [PubMed: 12652000]
Mason JW. A review of psychoendocrine research on the sympathetic-adrenal medullary system.
Psychosom Med 1968;30(Suppl):631–653. [PubMed: 4974233]
Mastorakos G, Ilias I. Maternal and fetal hypothalamic–pituitary–adrenal axes during pregnancy and
postpartum. Ann N Y Acad Sci 2003;997:136–149. [PubMed: 14644820]
Matthews KA, Rodin J. Pregnancy alters blood pressure responses to psychological and physical
challenge. Psychophysiology 1992;29:232–240. [PubMed: 1635966]
McNair, DM.; Loor, M.; Droppleman, LF. Profile of mood states. San Diego, CA: Educational and
Industrial Testing Service; 1981.
Murphy VE, Smith R, Giles WB, Clifton VL. Endocrine regulation of human fetal growth: The role of
the mother, placenta, and fetus. Endocr Rev 2006;27:141–169. [PubMed: 16434511]
Nierop A, Bratsikas A, Klinkenberg A, Nater UM, Zimmermann R, Ehlert U. Prolonged salivary cortisol
recovery in second-trimester pregnant women and attenuated salivary alpha-amylase responses to
psychosocial stress in human pregnancy. J Clin Endocrinol Metab 2006a;91:1329–1335. [PubMed:
16434458]
ENTRINGER et al. Page 12
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Nierop A, Bratsikas A, Zimmermann R, Ehlert U. Are stress-induced cortisol changes during pregnancy
associated with postpartum depressive symptoms? Psychosom Med 2006b;68:931–937. [PubMed:
17132840]
Nijland MJ, Ford SP, Nathanielsz PW. Prenatal origins of adult disease. Curr Opin Obstet Gynecol
2008;20:132–138. [PubMed: 18388812]
O’Brien GD, Queenan JT, Campbell S. Assessment of gestational age in the second trimester by real-
time ultrasound measurement of the femur length. Am J Obstet Gynecol 1981;139:540–545.
[PubMed: 7193418]
O’Donnell K, O’Connor TG, Glover V. Prenatal stress and neurodevelopment of the child: Focus on the
HPA axis and role of the placenta. Dev Neurosci 2009;31:285–292. [PubMed: 19546565]
Odagiri E, Ishiwatari N, Abe Y, Jibiki K, Adachi T, Demura R, Demura H, Shizume K. Hypercortisolism
and the resistance to dexamethasone suppression during gestation. Endocrinol Jpn 1988;35:685–690.
[PubMed: 3220047]
Pruessner JC, Wolf OT, Hellhammer DH, Buske-Kirschbaum A, von Auer K, Jobst S, Kaspers F,
Kirschbaum C. Free cortisol levels after awakening: A reliable biological marker for the assessment
of adrenocortical activity. Life Sci 1997;61:2539–2549. [PubMed: 9416776]
Radloff LS. The CES-D scale: A self-report depression scale for research in the general population. Appl
Psychol Meas 1977;1:385–401.
Raudenbush, SW.; Bryk, AS. Hierarchical linear models: Applications and data analysis methods.
Thousand Oaks: Sage Publications; 2002.
Rice D, Barone S Jr. Critical periods of vulnerability for the developing nervous system: Evidence from
humans and animal models. Environ Health Perspect 2000;108(Suppl 3):511–533. [PubMed:
10852851]
Sandman CA, Glynn L, Schetter CD, Wadhwa P, Garite T, Chicz-DeMet A, Hobel C. Elevated maternal
cortisol early in pregnancy predicts third trimester levels of placental corticotropin releasing hormone
(CRH): Priming the placental clock. Peptides 2006;27:1457–1463. [PubMed: 16309788]
Sasaki A, Shinkawa O, Yoshinaga K. Placental corticotropin-releasing hormone may be a stimulator of
maternal pituitary adrenocorticotropic hormone secretion in humans. J Clin Invest 1989;84:1997–
2001. [PubMed: 2556451]
Schulte HM, Weisner D, Allolio B. The corticotrophin releasing hormone test in late pregnancy: Lack
of adrenocorticotrophin and cortisol response. Clin Endocrinol (Oxf) 1990;33:99–106. [PubMed:
2169361]
Shea AK, Streiner DL, Fleming A, Kamath MV, Broad K, Steiner M. The effect of depression, anxiety
and early life trauma on the cortisol awakening response during pregnancy: Preliminary results.
Psychoneuroendocrinology 2007;32:1013–1020. [PubMed: 17855000]
Singer, JD.; Willett, JB. Applied longitudinal data analysis: Modeling change and event occurrence. New
York: Oxford University Press; 2003.
Snijders TAB, Bosker RJ. Modeled variance in two-level models. Sociol Methods Res 1994;22:342–363.
Van den Bergh BR, Mulder EJ, Mennes M, Glover V. Antenatal maternal anxiety and stress and the
neurobehavioural development of the fetus and child: Links and possible mechanisms. A review.
Neurosci Biobehav Rev 2005;29:237–258. [PubMed: 15811496]
Wadhwa PD. Psychoneuroendocrine processes in human pregnancy influence fetal development and
health. Psychoneuroendocrinology 2005;30:724–743. [PubMed: 15919579]
Wadhwa PD, Sandman CA, Garite TJ. The neurobiology of stress in human pregnancy: Implications for
prematurity and development of the fetal central nervous system. Prog Brain Res 2001;133:131–142.
[PubMed: 11589126]
Wadhwa PD, Garite TJ, Porto M, Glynn L, Chicz-DeMet A, Dunkel-Schetter C, Sandman CA. Placental
corticotropin-releasing hormone (CRH), spontaneous preterm birth, and fetal growth restriction: A
prospective investigation. Am J Obstet Gynecol 2004;191:1063–1069. [PubMed: 15507922]
Weinstock M. The long-term behavioural consequences of prenatal stress. Neurosci Biobehav Rev
2008;32:1073–1086. [PubMed: 18423592]
Wilhelm I, Born J, Kudielka BM, Schlotz W, Wust S. Is the cortisol awakening rise a response to
awakening? Psychoneuroendocrinology 2007;32:358–366. [PubMed: 17408865]
ENTRINGER et al. Page 13
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Wolfe LA, Weissgerber TL. Clinical physiology of exercise in pregnancy: A literature review. J Obstet
Gynaecol Can 2003;25:473–483. [PubMed: 12806449]
Wust S, Federenko I, Hellhammer DH, Kirschbaum C. Genetic factors, perceived chronic stress, and the
free cortisol response to awakening. Psychoneuroendocrinology 2000;25:707–720. [PubMed:
10938450]
ENTRINGER et al. Page 14
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Figure 1.
Mean HR (±SEM) and MAP (±SEM) values before, during, and after the TSST in pregnant
women (n = 148) and in the CG (n = 36) for both study assessments. To graphically illustrate
the findings of the three-level HLM models, percent increase (±SEM) from baseline is depicted
for HR and MAP for both groups. Significant differences (p < 0.05) are indicated with an
asterisk.
ENTRINGER et al. Page 15
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Figure 2.
Mean distress levels (±SEM) before and after the TSST in pregnant women (n = 148) and in
the CG (n = 36) for both study assessments. Significant differences (p < 0.05) are indicated
with an asterisk.
ENTRINGER et al. Page 16
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Figure 3.
Mean (±SEM) salivary cortisol concentrations in response to awakening (CAR) and over the
course of the day in pregnant women (n = 148) and in the CG (n = 36) for both study
assessments. To graphically illustrate the findings of the three-level HLM models, percent
increase (±SEM) from awakening is depicted for both groups. Significant differences (p < 0.05)
are indicated with an asterisk.
ENTRINGER et al. Page 17
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
ENTRINGER et al. Page 18
Table I
Study characteristics for age, race/ethnicity, education, marital status, BMI and parity for pregnant group (PG,
n = 148) and (CG, n = 36) subjects, as well as p-values for comparisons between the two groups.
PG CG P
Age (years ± SD) 28.5 ± 6.0 32.0 ± 7.0 < 0.01
Race/ethnicity n.s.
Non-Hispanic White 39% 36%
Hispanic White 30% 25%
Hispanic other 10% 11%
Non-Hispanic Black 5% 6%
Non-Hispanic Asian 7% 11%
Non-Hispanic other 9% 11%
Years of school completed 14.5 ± 2.5 14.0 ± 3.0 n.s.
Married 83% 78% n.s.
BMI (pre-pregnancy BMI for pregnant group) 25.5 ± 6.1 25.9 ± 7.3 n.s.
Nulliparous 46% 51% n.s.
n.s., non-significant.
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
ENTRINGER et al. Page 19
Table II
Hierarchical linear model estimates for effects of time and gestational age at test predicting HR (a) and MAP (b)
measurements.
Parameter SE P
(a) HR (beats/min)
Intercept 78.97 0.838 < 0.001
Time 2.207 0.165 < 0.001
Time2−0.1009 0.0075 < 0.001
Intercept × gestational age at test 0.5151 0.0617 < 0.001
Time × gestational age at test −0.0509 0.0097 < 0.001
Time2 × gestational age at test 0.0021 0.0004 < 0.001
(b) MAP (mmHg)
Intercept 76.85 1.052 < 0.001
Time 2.299 0.188 < 0.001
Time2−0.1020 0.0091 < 0.001
Intercept × gestational age at test 0.0764 0.0647 0.239
Time × gestational age at test −0.0431 0.0149 0.005
Time2 × gestational age at test 0.0018 0.0007 0.012
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
ENTRINGER et al. Page 20
Table III
Explained session-by session variance (R2) for changes in HR, MAP, and distress from TSST 1 to 2 for the
pregnant group (PG, n = 148) and the (CG, n = 36).
R2 (for session-by-session variance) PG CG
HR 0.47 0.00
MAP 0.10 0.05
Distress 0.19 0.04
Stress. Author manuscript; available in PMC 2010 May 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
ENTRINGER et al. Page 21
Table IV
Hierarchical linear model estimates for effects of time (CAR and course of the day) and stage of gestation
predicting salivary cortisol concentrations.
Diurnal Cortisol [ln (nmol/L) + 1]
Parameter SE P
Intercept 2.901 0.047 < 0.001
Time (CAR) 0.9128 0.1359 < 0.001
Time2 (CAR) −0.7087 0.1030 < 0.001
Time (course of day) −0.1319 0.0140 < 0.001
Time2 (course of day) 0.0012 0.0010 0.219
Intercept × gestational age at test 0.0188 0.0041 < 0.001
Time (CAR) × gestational age at test −0.0321 0.0105 0.003
Time2 (CAR) × gestational age at test 0.0250 0.0079 0.002
Time (day) × gestational age at test 0.0023 0.0012 0.074
Time2 (day) × gestational age at test −0.0001 0.0001 0.605
Stress. Author manuscript; available in PMC 2010 May 3.
