Document 15055

CHANGES IN BASAL BODY TEMPERATURES
AND THE PREDICTION OF THE
ONSET OF LABOR
by
Caron Candace Campbell
A thesis submitted to the faculty of
The University of Utah
in partial fulfillment of the requirements for the degree of
Master of Science
College of Nursing
The University of Utah
August 1982
G)1982 Caron Candace Campbell
All Rights Reserved
THE UNIVERSITY OF UTAH CRADUATE SCI-IOOL
SUPERVISORY COMMITTEE APPROVAL
of a thesis submitted by
Caron Candace
Campbell
This thesis has been read by each member of the following su pervisory committee and by m�jorit y
vote has been fou nd to be satisfactory.
THE UNIVERSITY OF UTAH GRADUATE SCHOOL
FINAL READING APPROVAL
To the Graduate Council of The University of Utah:
I have read the thesis of
Caron Candace Campbell
In Its
final form and have found that (I) its format, citations, and bibliographic style are
consistent and acceptable; (2) its illustrative materials including figures, tables, and
charts are in place; and (3) the final manuscript is satisfactory to the Supervisory
Committee and is ready for submission to the Graduate School.
Date
Lorraine Sevcovic,
M.S.,
Member. Supervisory Committee
Approved for the Major Department
Linda K.
Amos,
Ed.D.,
F.A.A.N.
Chairman! Dean
Approved for the Graduate Council
James L. Clay to
Dean or The
Graduate
Schoo1
C.N.M.
ABSTRACT
Pregnant women were requested to chart daily basal
body temperatures from the 37th week of gestation until
the birth of their infants in order to examine whether
changes in basal body temperatures occur in relationship
to the spontaneous onset of labor in such a way the labor
can thus be predicted.
Thirty-five women entered the study, resulting in 3
vaginal temperature and 16 oral temperature charts which
met criteria for spontaneous labor.
Mean vaginal and
oral temperatures did not differ significantly.
Charts meeting criteria for spontaneous onset of
labor were analyzed for significant changes in basal
body temperatures with the cumulative sum (CUSUM) test.
Nine charts (47.4%) had erratic patterns with no significant changes in baseline basal body temperatures.
Five charts (26.3%) demonstrated a significant drop in
temperature 2-6 days (mean=3.4 days) before the onset
of labor.
Four charts (21.1%) had a significant drop
16-19 days (mean=17.5 days) prior to labor.
One chart
(5.2%) signalled a drop 30 days before labor.
Changes in basal body temperatures observed in
these subjects have too much individual variation to
support the use of temperature charting and analysis
as a tool which can predict the spontaneous onset of
labor.
v
CONTENTS
ABSTRACT. . . .
ACKNOWLEDGMENTS .
iv
. viii
Chapter
I.
II.
INTRODUCTION • •
1
Purpose . . .
. • •
Conceptual Framework • •
Review of Literature • • • • •
Swine • . . • •
Dogs . • • • •
Sheep.
. ••
Goats.
Cattle . . • • . . • • .
Primates .
Women. • •
Research Questions • . . • • •
2
3
5
6
6
7
7
8
8
8
8
METHODOLOGY.
10
Subjects . . • • • •
• • .
Definitions • . . • • •
••• • • •
Basal Body Temperature • • • •
Term Pregnancy • • • • .
Onset of Spontaneous Labor • .
Data Collection Procedures • • • • •
Assumptions . . . • • .
10
10
10
10
DATA ANALYSIS • .
14
IV.
RESULTS . •
17
V.
DISCUSSION.
27
Research Question One .
Research Question Two • .
. • .
Progesterone and Thermoregulation in
Pregnancy. . • • . •.• . . . • • • .
27
27
III.
11
11
13
28
VI.
SUMI~RY
.
31
Appendices
A.
INSTRUCTIONS TO PARTICIPANTS.
B.
BASAL BODY TEMPERATURE CHART.
REFERENCES
• .
.
.
.
. • .
• • • .
vii
.
33
.
.
.
• .
.
36
• • • .
39
ACKNOWLEDGMENTS
This thesis was a delightful experience thanks to
the support and teaching of special individuals.
I wish
to credit Mary Anne Graf, M.S., C.N.M., for the original
idea for this study, which arose out of discussions
about her very fertile Samoyed, Delight.
I am partic-
ularly grateful to Richard Worley, M.D., who guided me
through the fascinating intricacies of reproductive
endocrinology.
Dr. Worley also offered encouragement
and constructive suggestions throughout this process
which enhanced my learning and improved the quality of
this work immeasurably.
I
wish to express appreciation
of Marlene Egger, PhD., who patiently helped me interpret the CUSUM test and generously shared her time
and equipment for the data analysis.
Lorraine Sevcovic,
M.S., C.N.M. has my gratitude for doing all those things
a chairperson must do while maintaining enthusiatic
support.
Special thanks to Sid Spencer of Bergen-Brunswig
Drug Company for supplying basal body temperature thermometers for the study.
CHAPTER I
INTRODUCTION AND REVIEW
OF LITERATURE
Many attempts have been made to predict precisely
when labor and birth will occur.
A due date or estimated
date of confinement (EDC) is computed using the mean
duration of normal pregnancy, known to be 280 days
past the last normal menstrual period (LNMP).
The range,
however, is between two weeks before and two weeks after
the EDC.
Signs and symptoms of impending labor often observed
in women are lightening, cervical changes, false labor,
premature rupture of membranes, bloody show, an energy
spurt, and gastrointestinal upsets (Varney, 1980).
Un-
fortunately, these signs and symptoms may appear any time
from hours to weeks before true labor begins.
In mammals, similar changes are observed before
parturition:
relaxation of pelvic ligaments, mucoid dis-
charge, vulvar swelling, restlessness, soft or' more fre-'
quent stools, and a change in body temperature.
In some
species, the change in body temperature is predictive
2
within hours of the onset of parturition.
Whether or not changes in basal body temperature
(BBT) in women occur prior to the onset of labor is
unknown.
If there is a detectable shift in BBT which
is consistent in its relationship to the onset of labor,
it may prove a valuable tool to aid management of care
and preparation for labor and birth.
For example, pregnant women and their families
could initiate contingency plans for child care, household maintenance,
and
wor k absences.
Adequa te rest
and nutrition could be encouraged, and anxieties stemming
from uncertainties about labor onset may be eased, so
that labor is entered in a well-rested, relaxed state.
Care providers could assure completeness of antenatal
care and education, and revise plans as necessary.
They
could inform hospitals or birth centers of the client's
status and confirm that antenatal records were up-to-date
and available.
Knowledge that labor is imminent could
allow the freedom to await spontaneous labor rather than
inducing labor in some cases.
Thus, the ability to
predict the onset of labor may have broad economic, sociological, psychological, and medical ramifications •
. P'u:rpo'Se
The purpose of this study was to examine the rela-
3
tionship between basal body temperature and the spontaneous onset of labor in women at term.
Conceptual Framewo'r k
Body temperature is a balance between heat loss
and heat production, which in mammals is regulated in
the central nervous system by the hypothalamus.
The
hypothalamus operates as a thermostat which is influenced
by a complex interaction of chemical, environmental, and
hormonal inputs.
One hormone known to affect BBT,
apparently by a direct effect on the hypothalamus, is
progesterone.
The thermogenic effects of progesterone are responsible for the rise in BBT observed in the luteal phase
of ovulatory menstrual cycles in women.
As the plasma
progesterone concentration increases following ovulation,
so also does the BBT.
Conversely, when progesterone
concentration falls at the end of a cycle, the BBT returns
to the preovulatory baseline.
If conception and implantation occur during a cycle,
the elevated plasma progesterone concentration is maintained by the corpus luteum, and the BBT remains at or
above the postovulatory level.
Later in pregnancy, the
placenta becomes the site of progesterone production,
and plasma concentration continues to rise gradually until
4
delivery (Pritchard & MacDonald, 1980).
In many animal species, the plasma progesterone
concentration is known to fall prior to the onset of
labor and is believed to play an important role in
the initiation of labor (Tulchinsky & Ryan, 1980).
Not surprisingly, a decline in body temperature has been
observed following a drop in progesterone concentration.
For example, in the bitch progesterone falls sharply
36-48 hours prepartum, followed by a decline in body
temperature 24 hours before parturition (Concannon, Powers,
Holder
& Hansel, 1977).
Similar declines in plasma
progesterone and body temperature associated with imminent
parturition have been documented in cows and ewes (Ewbank,
1969; Winfield, Makin
Concannon et
&
Williams, 1973; Dufty, 1971;
al., 1977).
Declines in progesterone and body temperatures are
not a universal finding in mammals, however.
In nonhuman
primates and women plasma progesterone concentrations
do not routinely fall prior to the onset of labor
(Walsh
& Novy, 1981; Boroditsky, Reyes, Winter & Faiman, 1978;
Tulchinsky & Ryan, 1980), although there is speculation
that alteration of the metabolism of the hormone in the
maternal or fetal compartment may be occurring.
sky and Ryan suggested
that
Tulchin-
a fall in hormone levels
in the uterus may not be reflected in plasma concentra-
5
tion, or that there are other cellular determinants
involved, such as receptor availability.
By the same logic, it is also conceivable that
there may be changes in receptor availability in the
hypothalamus which account for declines in body temperature before labor, even when the plasma progesterone
concentration remains elevated.
Thus, it is appropriate
to wonder if women may exhibit changes in BBT associated
wi th immine.nt labor in spi te of unchang ing plasma progesterone concentrations.
Revi'e'w' of' 'Li'te'r'atu'r e
Observations of preparturient body temperature
changes have appeared in veterinary literature for many
decades.
Weisz (1943) reviewed Austrian and German
veterinary journals and concluded that cows, mares, does,
goats, sows, and dogs had distinct decreases in body
temperatures within a day or two of parturition; sheep
and cats had declines that were too indistinct for practical purposes.
Research during the last dozen years has provided
scientific documentation of changes in body temperature
and its relationship to parturition in the following
species:
6
Swine
Hendrix, Kelley, Gaskins, and Bendel (1978) found
o
an increase of O.4 Cin rectal temperatures beginning 4
hours before parturition.
Littledike, Witzel, and Riley
0
(1979) observed an increase of 1. 4 C beg inning approximately 12 hours before the birth of the first pig.
Similarly, Elmore, Martin, Riley, and Littledike (1979)
0
noted an increase of 0.6-1. 2 C in farrowing swine 13 +4.1
hours before parturition.
Conversely, King, Willoughby, and Hacker (1972)
observed a subnormal temperature for at least one week
prior to farrowing, ascribing the increase in rectal
temperatures coincidental with labor to the sows'
creased activity levels.
in-
They concluded that rectal
temperatures could not be used to predict farrowing.
Research on dogs has produced similarly varying
results.
Kirk, McEnter, and Bentinck-Smith (1968) des-
cribed a "decided drop in rectal temperature" at the onset
of labor, but did not quantify the decrease other than to
note that it may be as low as 98 o F.
Griesemer and Gibson
(1963) used the observed drop in rectal temperature as
well as other signs to time the operative deliveries of
gnotobiotic (germ-free) dogs.
Concannon, Powers, Holder, and Hansel (1977) dis-
7
covered a distinct transient hypothermia in 78/80 bitches
which occurred 8-24 hours prior to parturition.
However,
Long, Mezza, and Krakowka (1978) concluded that a drop
in rectal temperature was of some value, but too variable
among individuals to be used as the sole criterion for
predicting impending labor.
Sheep
Ewbank (1969) found a consistent drop in temperatures
of sheep in the 54 hours preceding lambing, but individual
variation prevented accurate pinpointing of the exact
time of parturition.
Winfield, Makin, and Williams
(1973) measured temperatures at different times of day
and discovered that early morning temperatures showing
a fall of O.3 0 C or greater from previous consecutive monning readings indicated that parturition was imminent.
Their research also confirmed Ewbank's findings.
Goats
Jones and Knifton (1971) failed to demonstrate any
obvious or uniform temperature changes in goats which
could be used to predict the first stage of labor.
Cattle
Dufty (1971) observed a fall in rectal temperatures
immediately prior to parturition, but commented that
8
they were highly variable and frequently confused
with normal daily fluctuations, and thus were not useful
as a diagnostic tool.
Pr imates
Ruppenthal and Goodlin (1981) noted dramatic declines
in temperatures measured by subcutaneous temperature
transmitters in pig-tailed macaques (M'aca'c'a' n'em'estrina)
1-2 hours prior to the expulsion of fetuses.
Women
Changes in basal body temperatures of women have
been studied extensively during the menstrual cycle, but
not during full-term pregnancy.
Burd (1977) investigated
mammary temperatures as measured by thermograms for 29
days preceding parturition, and found no significant
changes until the first postpartum day.
In a self-report,
Yewlett (1979) outlined the results of temperatures taken
0
daily during her pregnancy which showed a O.3 C drop 4
days before spontaneous labor with her second child.
Goodlin (1981) reviewed daily temperatures of hospitalized women at term, but found no significant changes
before labor began.
Research Questions
1.
Is there a change in basal body temperature related
9
to the spontaneous onset of labor in women at term?
2.
Can observation of basal body temperatures in women
at term permit clinically useful predictions of the
onset of spontaneous labor?
CHAPTER II
METHODOLOGY
Subjects
Thir:ty-five women participated in the research.
Of these, 14 (40%) volunteered during prenatal visits
in private obstetrical practices.
The remaining 21
subjects (60%) were volunteers from late pregnancy
childbirth education classes.
Basal Body Tempe'ra'tu're
Basal Body Temperature (BBT) is conceptually defined as the measurement of heat being produced by the
body at complete rest as a result of basal metabolic
activity.
BBT is operationally defined as the oral or
vaginal temperature taken before any activity after at
least four hours of consecutive sleep.
Term Pregnancy
Term Pregnancy is defined both conceptually and
operationally as a pregnancy that has advanced beyond
38, but not more than 42 weeks of gestation completed
since the first day of the last normal menstrual period
11
(LNMP).
For the purpose of this investigation, if the
LNMP was unclear, the estimated date of confinement
(EDC) determined by the care provider was considered 40
weeks of gestation completed.
Onset of Spontaneous Labor
Onset of spontaneous labor is defined conceptually
as spontaneous uterine contractions of sufficient fre·"'t
quency, intensity, and duration to bring about readily
demonstrable effacement and dilatation of the cervix.
The operational definition is the spontaneous occurrence
of regular uterine contractions accompanying cervical
changes validated by a care provider or health care
personnel which result in birth of the child within 36
hour s.
Da ta CoTlection P'roc'edu'r'es
Subjects were instructed to take and record daily
temperatures at the same time every day after at least
4 hours consecutive sleep whenever possible.
They were
asked to note interruptions of sleep, fever or illness,
medications other than vitamins or iron, or anything
unusual which they thought might have affected their
temperatures.
12
In addition to daily temperatures, subjects recorded
the following information about their labors and births:
date and time of onset of regular contractions, date
and time of rupture of membranes and whether rupture
was spontaneous or artificial, time of admission to the
hospital, time and date of the birth, type of delivery
(vaginal/forceps/cesarean), and medications used during
labor (including pitocin and epidural anesthesia).
The
subject's gravidity, parity, age, LNMP, and EDC were
also recorded on the chart.
Subjects were provided with written instructions
(Appendix A), BBT charts (Appendix B), Becton-Dickinson
Basal Temperature thermometers, and a stamped envelope
addressed to the investigator for returning completed
charts.
Subjects were checked for ability to read the
basal thermometer accurately.
Each subject was given a date to begin recording
temperatures which was either the day that 37 weeks of
gestation had been completed since the LNMP, or 21 days
before the EDC as determined by other means such as
sonography or clinical estimates in those cases where
the LNMP was unclear.
This was to allow at least a
week of baseline temperature recordings in women who
truly delivered at term.
Confidentiality was protected by coding charts with
13
the number of the individual's consent form.
The con-
sent forms recorded the subject's address and phone number.
Interested subjects were promised a summary of the
outcome of the study.
Assumptions
Accuracy of the thermometers and the subjects' recording of temperatures was assumed.
The assumption was
also made that the temperatures noted by sujects were accurate measrues of basal temperatures, whether taken
orally or vaginally, if taken according to the instructions.
CHAPTER III
DATA ANALYSIS
Charts were analyzed for significant changes in BBT's
using the cumulative sum (CUSUM) test, which has been
shown to be a reliable statistical method for detecting
BBT shifts in ovulatory menstrual cycles (Royston &
Abrams, 1980).
Xl' x 2 ·
In the CUSUM test, sequential values
• .x r '· • .x N of BBT's are examined to detect a
shift in the mean BBT's beyond a baseline value of B.
If the mean E(X) of subsequent BBTls is less than B,
these negative deviations predominate and a significant
change in BBT is signalled.
where
The change of interest in E(X) is
=
var (X).
~
2
A hypothesis test is applied in which the
null hypothesis H : E(X)
o
alternative HI: E(X)
=B
>
--
B is tested against an
S~.
CUSUM's are calculated
as cumulative deviations of the sample BBT values X
r
about B - ~
scr ,
which is a central reference value.
The CUSUM test is performed as follows:
the CUSUM derived from sample values x
rule,
r
let s
r
be
according to the
15
=
0,
=
min (0, Sr-l
+
Xr
r
HO is rejected if Sr
<
h
=
0-
,
(b -
~
Ej v
).
1,2, . . . , N
the decision interval,
and a significant drop in E(X) is judged to have occurred.
In this application of the CUSUM test, B is the
mean of the first three temperature readings, or three
other sequential readings which were more representative
of the baseline if the first three readings were uncharacteristic of the majority of readings. (An alternative
sequence is indicated by a bar above the graphs in
Figures one through three).
The critical value h was
calculated to yield an overall significance level of
~
=
6
(j"
.05.
The magnitude of the change of interest
was set at
o. SOF.
Since CUSUM's that are calculated indefinitely will
eventually signal a shift, an estimated run length L is
programmed into the test.
For example in average men-
strual cycles this value L is set at 12.
L was set at 17 based on
In this study,
findings in the literature
that suggested a change in temperature may occur within
4 days of labor.
Since these subjects began recording
temperatures at 37 weeks gestation, or 21 days before
16
their EDC's, L was calculated by subtracting 4 from 21.
Temperatures that were apparently influenced by
interruptions or alterations in sleep patterns, medications, illness, or other unusual events noted by the
subjects were omitted from the CUSUM calculations.
Significance of differences observed between groups
was determined using the t-test.
CHAPTER IV
RESULTS
From the 35 subjects 19 charts (54%) were received
which met the criteria of uncomplicated pregnancy and
spontaneous onset of labor.
Of the remaining 16 subjects,
5 (14%) delivered before 37 weeks gestation, 1 (3%) was
induced, 1 (3%) was on bedrest for 19 days prior to the
onset of labor, 1 broke her thermometer but did not request another, 1 (3%) had a thermometer that "didn 1 t
work" but did not request another.
One (3%) stopped tak-
ing her temperature after her due date passed, 1 (3%) was
still undelivered at the time of data analysis, and 5
(14%) failed to respond to mail or phone inquiries
(see Ta ble 1).
Eleven subjects agreed to take vaginal temperatures;
3 (27%) charts were returned.
Of the remaining 8 subjects,
3 delivered early, 1 had a broken thermometer, 1 stopped
taking her temperatures, and 3 did not respond to
in~
quiries (see Table 2).
Twenty-four subjects agreed to take oral temperatures, from whom 16 charts (67%) could be used for
analysis.
Of the 8 remaining subjects, 1 was induced,
18
Table 1
Outcomes for Subjects Participating in the Study
N
%
Subject Numbers
19
54%
6,8,9,11,13,15,16
17,20,21,22,23,25,
26,27,28,31,33,35
Induction
1
3%
18
Bedrest
1
3%
32
Thermometer failure
1
3%
24
Broken thermometer
1
3%
3
Delivered early
5
14%
4,19,12,2,30
No response
5
14%
1,5,7,29,34
Quit taking temps
1
3%
10
Undelivered
1
3%
14
35
100%
Acceptable charts
Total
19
Table 2
Outcomes for Subjects Taking Vaginal Temperatures
Percentage
3/11
Acceptable charts
27%
8/11
Not available
73%
3 delivered early
3 no response
1 quit taking temps
1 broken thermometer
20
1 was undelivered, and 2 failed to respond to inquiries.
(see table 3).
From the 14 subjects recruited' from private prac+
tices, 6 charts (43%) met criteria for analysis.
The
remaining 8 were the same subjects lost from the vaginal
temperature group.
From the 21 subjects recruited in childbirth classes,
13 charts (61%) met criteria for analysis.
The remaining
8 subjects were the same ones lost from the oral temperature group.
The ages of all subjects ranged from 16-34, with
the mean age being 24.78 years (SO=3.87).
Of the 19
charts used for analysis, the subjects' ages ranged 1930, with a mean of 24.84 years (SO=3.2).
The difference
was not significant.
Fifteen primiparous and 4 mUltiparous women returned
charts that met the criteria for analysis.
Oata is
incomplete on the parity of the remaining subjects because that information was generally not recorded on the
consent forms in addition to the charts.
Temperatures on the charts ranged between 96.3 0 and
0
98.5 0 F, with an average mean temperature of 97.71 F
(SO=0.195) .
o
The average standard deviation was 0.24 F.
Vaginal temperatures were not significantly different
than oral temperatures.
21
Table 3
Outcomes for Subjects Taking Oral Temperatures
Percentage
16/24
Acceptable charts
67%
8/24
Not available
23%
2 delivered early
2 no response
1 undelivered
1 thermometer failure
1 induction
1 bedrest
22
Among the charts analyzed by the CUSUM test 9/19
(47.4%) had erratic patterns with no demonstrable changes
in BBT (Figure 1).
Five charts (26.3%) showed a significant change in
BBT 2-6 days prior to the onset of labor.
terval was 3.4 days (SD=1.95).
The mean in-
All the subjects were
primiparous (Figure 2).
Four charts (21.1%) signalled significant changes
16-19 in BBT days before labor, the mean being 17.5
days (SD=1.29)
Of these four subjects, 2/4 (50%) were
primiparous and 2/4 (50%) were multiparous.
(Of interest
is chart #32, which also showed a significant drop 19
days before spontaneous labor.
However, the confounding
influence of the subject's bedrest eliminated this chart
from formal analysis)
(Figure 3).
One chart (5.2%) had a significant drop in temperature 30 days before spontaneous labor
(Figure 4).
In several cases (#11, 15, 23, 26, and 31) the BBT
rose again after the significant drop signalled by the
CUSUM test, either in isolated spikes or a gradual increase as labor became imminent.
There was no relationship between a drop in BBT
and the EDC.
t-rj
...,-
I.Q
C
11
m
I--'
ttl
11
t1
III
rt
t-'-
n
tlj
tIl
1-3
t"O
III
rt
rt
m
t1
::l
en
I'V
W
24
Days since 37th week of gestation
,
I
:
of
I,
,
...~~
98
'
'
.: .
-".
86
Ix
,t...--i '
I
'It:
i'
,
)
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I
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I
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115
•
..
:
;
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'"
,
:
:
~
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It;
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!
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t
j,
••
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98
:":1\"::
-----. --+~ ., l'
.l:
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86
,
Figure 2.
I
,
i
I
!,
BBT Decline 2-6 Days Before Labor
I
I
i
25
Days since 37th week
I
ge~tati9n
I
I
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.. X
I
I
·w
98
: f
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97
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: . 1::1
96
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r'
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98
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• i. ;,
: i. i: :::!: I' . . I:: ~ :
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.' .. . :":'.:. .... ~ .... L:..:.:..:.++.~-+-..;.. . . . . .-+-; .; ~ .' I;';::'" ! .
98
.:.~..
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--7-:'-',
1
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---~-.
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i
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na~led
--'r ='aay'-cif -,.!=-.-+...;....j.--
I
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... I· .
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=
:.. !i .
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~.~~~~.~----~--~----~
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i9-
st· .
"'--1
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Figure 3.
I
~
. j
BBT Decline 16-19 Days Before Labor
i
i
26
98
97
Figure 4.
BBT Decline 30 Days Before Labor
CHAPTER V
DICUSSSION
Research Question One
"Is there any change in BBT related to the spontaneous onset of labor in women at term?"
The data offer
some intriguing information, but no definitive answer
to this question.
Apparently some women demonstrate a
significant drop in BBT at the end of pregnancy, but a
relationship to the onset of labor is merely suggested
rather than clearly defined.
Research Question Two
"Can observation of BBT's in women at term permit
clinically useful prediction of the onset of spontaneous
labor?"
Two apparent patterns of BBT changes in half
the women studied is not strong evidence to support routine BBT charting for the prediction of labor.
That
only half the women showed any changes at all makes
BBT's no
more predictive than many other traditionally
observed signs and symptoms of impending labor.
28
Progesterone and Thermoregula'tion
in Pregnancy
The thermogenic effects of progesterone in menstrual cycles is observed in the upward shift in BBT's
which occurs as plasma progesterone concentrations
increase abruptly during the luteal phase of the cycle.
When a pregnancy occurs, plasma progesterone concentration increases steadily from 23-54 ng/ml in the first
trimester to 120-180 ng/ml in the third trimester
(Tulchinsky & Ryan, 1980).
However, the BBT does not
appear to continue increasing as pregnancy progresses.
The mean BBT of these subjects was actually LOWER than
the BBT usually observed in women during the luteal phase
of the menstrual cycle (97.71
0
vs
>
0
98.0 F).
The response of the hypothalamus to the thermogenic
effects, of progesterone is apparently not related directly
to plasma concentration, or we would expect elevations
in BBT's to parallel increases in plasma progesterone
concentration as pregnancy advances.
Inconsistencies among BBT patterns and a lower-thanexpected mean BBT in these subjects offer a great challenge to interpretation of the role of progesterone in
thermoregulation in women in late pregnancy.
uterine
irritability and labor occur in the presence of high or
variable plasma progesterone concentrations, perhaps as
29
a result of alterations in the availability of either
progesterone or its receptors in the myometrium.
That
only half the women studied demonstrated any change in
BBT prior to labor suggests that analogous changes in
thermoregulation by the hypothalamus, which might be
observed as a change in BBT, apparently do not occur at
the same time as the changes in myometrial activity.
There are several possible explanations for the
absence of a clearly defined change in BBT: 1) Perhaps
progesterone does not withdraw from the hypothalamus,
even though it may from the uterus and fetal membranes;
2) concentration of progesterone may decrease in hypothalamic tissues, but not below a threshhold necessary for
an observable change in BBT; or, 3) progesterone does
not withdraw from "any tissues, and an entirely different
mechanism is responsible for the changes in uterine
activity with the onset of labor.
Consideration must also be given to those cases
where a significant drop in BBT was followed by an
elevation in temperature as labor approached.
This
observation invites speculation about other factors
thought to be involved in both the onset of labor and
body temperature.
For example, there is compelling
evidence that an increase in local tissue levels of
prostaglandins is a common pathway for the activation
30
of normal labor, specifically PGE
sky & Ryan, 1980).
2
and
PGF2~
(Tulchin-
PGE 2 is also apparently an active
contributor to hypothalamic function and is involved in
fever production (Veale, Cooper & Pittman, 1978).
A
common side effect experienced by women administered PGE
2
for induction of labor is transient elevation in temperature (Southern, 1976).
Since prostaglandin release may
occur with or without a decline in plasma progesterone
(Tulchinsky & Ryan, 1980), elevations in temperature
observed after a drop may be a reflection of prostaglandin activity as labor becomes imminent.
The variability
among individual temperature patterns seems to add to
evidence that the onset of labor is a multifactorial
process rather than the result of a singular metabolic
pathway.
CHAPTER VI
SUMMARY
The results of this investigation do not strongly
support the observation of BBT's to predict the onset
of labor.
However, the discovery of two apparently
distinct patterns of change in the BBT's of some women
merits further investigation.
The experiences of this researcher lead to several
suggestions for improvement in future work with BBT's
in late pregnancy:
1)
Since so many women in this study delivered
before charting began, initiation of BBT observations
at 34 or 35 weeks' gestation would probably yield more
information, and perhaps offer some insight into
premature labors.
2)
Oral temperatures are apparently just as
accurate as vaginal temperatures, and have a higher
compliance rate among subjects.
3)
Selection of subjects from childbirth classes
is both more efficient for recruitment and results in
greater numbers of charts returned than with subjects
32
recruited individually from private prenatal visits.
3)
The baseline B in the CUSUM test should be
computed using the first 7 BBT readings, rather than
the first 3, in order to establish a more representative
baseline.
APPENDIX A
INSTRUCTIONS TO PARTICIPANTS
34
Instructions to Participants
Thank you for participating in this study of basal
body temperatures in women during the last few weeks
of pregnancy. No one has carefully studied temperatures
in pregnancy, so this study will add to our knowledge
about physiological changes in women as labor approaches.
The basal body temperature is the body's temperature
at complete rest and is especially accurate when taken
at the same time each day. Therefore, we ask that you
follow these guidelines as closely as possible.
1.
Take your temperature orally by inserting the basal
body temperature thermometer provided to you into
your mouth under your tongue. Leave the thermometer
in your mouth for a full three minutes before reading
the temperature.
2.
Take your temperature after at least four hours
consecutive sleep before beginning ANY activity;
this will be first thing in the morning before
rising for most women. Keep your thermometer at
your bedside so you don't have to rise to get it.
If, for some reason, your sleep was less than four
hours in a row, or you had interrupted sleep, take
your temperature anyway and make a notation in the
comments area of your chart. For example, if you
got up to the bathroom during the night, write
Uto bathroom" and try to note the time.
3.
Shake down your thermometer before going to sleep.
Look at the morning's reading one more time to double
check the accuracy of your charting.
4.
You may wash your thermometer with soap and COLD
water or alcohol. Generally, all you need to do is
simply wipe the thermometer with a clean tissue or
cloth after each use and store it in the container
it came in. Do NOT wash the thermometer in warm or
hot water.
5.
There are some other things you will need to write
in the comments area of your chart:
a.
b.
c.
Fever or illness
Any medications or drugs other than vitamins or
iron
Anything you think might have affected your
temperature
35
6.
Please note that we need information about your
labor and birth on the chart also.
This is just
as important as the daily temperatures.
7.
If you have any questions or concerns, or something
happens to your thermometer, please feel free to
contact me at (801) 466-7982.
APPENDIX B
BASAL BODY TEMPERATURE CHART
37
Instructions for Charting
To record the temperature for each day, place a solid
dot on the line for that temperature in the middle of the
box, like this:
Begin charting on the date written at the top of the
chart. This should be the day you complete 37 weeks of
gestation since your last period.
Write any comments in the long columns below the
temperature for that day. It is VERY important that I
have the following information as well for the study:
1. Regular, frequent contractions that were
confirmed as true labor by an internal, cervical exam began at
am/pm (time) on
(date). - -
------
2. Your bag of waters (underline) broke
spontaneously/was broken artificially at
am/pm (time) on
~~~----------------(date) .
3. You were admitted to the hospital
or birth center at
am/pm on
4. Your baby was born at
am/pm
on
(underline appropriate
descriptions) vaginal delivery/forceps/
cesarean. Reason for cesarean:
-----
5 •. Please list any medications or drugs
received before or during labor not already
charted in the comments area of your chart,
including epidural anesthesia or pitocin to
stimulate labor:
name of medication
time
date
38
All this information will be kept confidential. Your
chart will be identified by a code number. You may reach
me at
if you have any questions
or concerns.
Basal Body Temperature Chart
Begin charting on_____________________________________________
Oat~
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-- - f - ' - I - I - ' "
. 4--f--t---l!--1_+-+-+-+-.. t -
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1__ '
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comment
-!--·--li-·f-I--·'
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--- .
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---1-1- ,+ ..+""t-t ..
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..
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-
-
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40
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`