BBT, NOCTURNAL SLEEP AND OVULATION
Joseph Eldor, MD
Theoretical Medicine Institute, P.O.Box 12142, Jerusalem
91120, Israel
Abstract
Objective: To determine whether the basal body temperature
(BBT) is a reliable or not a reliable method for prediction
and detection of ovulation the literature was searched on
the procedure of obtaining the BBT in correspondence with
the new data in sleep medicine.
Results: The BBT tends to rise according to its circadian
rhythm at the time of awakening. Measuring the BBT at that
time will show not only the progesterone effect but also the
circadian effect.This can explain its "unreliability".
However, the lowest circadian thermogenic point during a
nocturnal sleep is at the 5th hour after sleep onset.
Measuring the temperature at this hour will show the
progesterone effect without the masking of the circadian
effect. This can make the BBT a reliable method for
ovulation prediction and detection.
Conclusions: A new basal body temperature measured at the
5th hour of a nocturnal sleep can pinpoint the rise at the
ovulation day without the masking effects of the circadian
rhythm, expressed in the old BBT recordings.
Key Words: Basal body temperature,progesterone,
norepinephrine, sleep, circadian rhythm.
It is almost eight years since the last publication
concerning basal body temperature (BBT) and ovulation
detection, in its title, appeared and listed in MEDLINE (1).
The question is whether this "unreliable" (2) method of
ovulation detection has still a place three years before the
year 2000 ?
Moghissi (3) examined in 30 normally menstruating women
their basal body temperature recordings and correlated it
with serum LH, progesterone and estradiol. In approximately
20% of ovulatory cycles the BBT failed to demonstrate
ovulation. Such poor reliability has been reported also by
Bauman (2) who found that only 22% of BBT assessments
corresponded to within 1 day of the biologic phenomena, and
by Buxton and Engle (4) who found at laparoscopies performed
on the first day of the BBT rise that in one third of cases
ovulation had already occurred more than 24 hours earlier.
A simple, reliable method to predict and detect ovulation in
women is still needed.
Introduction
Deep body temperature shows a strong circadian rhythm. It
varies in response to a variety of behavioral and external
stimuli, including sleep, physical activity, postural
changes, ambient temperature and meals. The menstrual cycle
of women also affects their temperature rhythm, with the
post-ovulatory temperature rise increasing the overall mean.
The relationship between the basal body temperature recorded
at awakening and the circadian temperature rhythm during
nocturnal sleep were evaluated in order to find the best
hour of basal body temperature recording that will reflect
mostly the peri-ovulatory temperature rise. Review of
relevant articles since 1838 reflected on one side the basal
body temperature`s way of recording and on the other side
the point that there is no exact determination of the best
hour of temperature recording after onset of a nocturnal
sleep. Review of articles on sleep revealed certain points
considering the basal body temperature with a suggestion for
the best hour of measuring the basal body temperature for
prediction and detection of ovulation.
Materials and methods
In order to review the literature concerning the basal body
temperature and temperature measurements during nocturnal
sleep the Medline was searched for any article mentioning
these items in its title or abstract. The references given
in each article were looked for articles that were published
before 1966, and are not included in the Medline. Articles
as late as 1838 were searched for any information on the
subject that can illustrate the technique of basal body
temperature recording. The relevant data was gathered to be
included in this review. The information on temperature
measurements during sleep was taken mainly from the journal
Sleep, and the references mentioned in its relevant
articles. By citing the various techniques used to measure
the basal body temperature and the temperature recordings
during sleep, the best time for basal body temperature
measurement was searched in order to exclude the other
circadian factors influencing it besides the progesterone
rise at the peri-ovulatory period.
The data was arranged by three main sections: basal body
temperature, progesterone and sleep. The connections between
these three factors seems essential to the evaluation of the
subject.
Basal body temperature
The basal body temperature graph is probably the most widely
used aid in the identification of the day of ovulation (3).
Von Fricke (5) studied in 1838 the axillary, vaginal and
uterine temperatures. His observations were made eight days
before the menses, four days before, and during the period.
He concluded that the vagina has a higher temperature than
either the axilla or the uterus, and that menstruation have
no influence upon the temperature. However, daily
observations were not made throughout the cycle.
Jacobi (6) studied in 1876 on six women, over a period of
two to three months, the oral, axillary, vaginal and rectal
temperatures. She confirmed the temperature rise before
menstruation and the fall during the flow to a level which
was lower than that of the intermenstrual period.
Rabuteau (7) reported in 1870 his study of a 28 year old
healthy woman with regular menstrual periods. He stated that
a drop in temperature occurred two days before menstruation
and disappeared several days after the cessation of the
flow.
Van de Velde (8) studied in 1905 the axillary temperature
in women, the number not stated. The typical curve showed a
premenstrual rise maintained for a short time, then a fall
before the onset of menstruation, and a continued drop
during and after menstruation to reach the lowest point
about ten days after cessation. He regarded the fall in the
temperature as the actual cause of menstruation. He said,
"it seems to me without doubt that an inner association
exists between the two facts - the beginning of the lowering
of the curve and the appearance of the menstrual bleeding -
an association indeed in the relationship of cause and
effect".
Flaskamp (9) postulated in 1928 that a double wave
temperature rhythm occuring during a day. The daily rhythm
showed a maximum between 5 and 8 P.M., and a minimum between
2 and 6 A.M.; a rise from 6 A.M. to noon; from 12 to 2 a
fall; the secondary rise from 2 to 6 P.M.; and a second fall
up to 6 A.M.
Tompkins (10) in 1944 stated the following procedure
utilizing temperature method for determining the date of
ovulation: "Take the temperature rectally with a blunt tip
rectal thermometer for five minutes by the clock immediately
after waking in the morning and before arising, eating,
drinking or smoking (!)" (the exclamation mark appeared in
the original article).Then he added that "some investigators
advise that the temperature be taken at the same hour each
morning. I myself would prefer to have the temperature
recorded when the patient wakes up in the belief that a more
significant figure is recorded at 10 a.m. on a Sunday
morning after a gay evening than at 7 a.m. when the patient
has only had three or four hours` sleep".
Barton and Wiesner (11) in their article on waking
temperature wrote that "a reading must be taken every
morning throughout the cycle, immediately on waking, before
rising, moving or taking food or drink".
Despite utilizing this procedure a discrepancy of up to 4
days between basal body temperature rise and ovulation time,
estimated by corpus luteum dating, was found (4,12,13).
Buxton and Engle (4) wrote in 1950 that "since only basal
body temperatures are indicative of the change produced by
ovulation it would theoretically be necessary to keep a
patient at complete basal rest and to take hourly
temperature readings to narrow down the ovulatory
temperature change more accurately".
Moghissi (14) in his review on prediction and detection of
ovulation, published in 1980, wrote that "a period of 6 to 8
hours of uninterrupted rest is deemed to be necessary before
the temperature reading is made".
Basal body temperature charts from menstrual cycles of 98
women were evaluated by six experienced physicians. The time
of ovulation was estimated from the charts by a consensus of
at least five of the evaluators coincided with the
luteinizing hormone peak ñ 1 day in only 17 (22.1%) of the
77 cycles that were determined by endocrine profiles to be
ovulatory and to have adequate luteal phases. Bauman (4),
from the Masters & Johnson Institute, St. Louis, Missouri,
who conducted this study concluded that the basal body
temperature was an "unreliable method of ovulation
detection".
McCarthy and Rockette (15) stated that "the prediction of
ovulation solely with the basal body temperature graph is
not useful because of the day-to-day variability of
temperature readings, cycle variability and the effects of
illness, medication, diet and changes in sleeping patterns".
Wetzels et al. (16), in 1982, compared the basal body
temperature with ultrasonographical findings for ovulation
detection in 47 cycles."Volunteers and patients were
carefully instructed to measure rectal temperature before
getting up each morning". They concluded that ovulation
detection and timing by basal body temperature were "not
reliable".
Weinberg and Cohen (17) from the IBM Thomas J. Watson
Research Center, Yorktown Heights, NY, published in 1983
their article on ovulation detection by monitoring
temperature during sleep. To measure the temperature they
used a stainless steel capped thermistor probe attached to a
feminine hygiene pad which was worn in the usual way as
during menstruation. The probe was resting against the skin
and no adhesives or pastes were used to improve thermal
contact. The probe had a long cable to a digital
thermometer. The thermometer was interfaced to a
microcomputer which recorded the data every 6 min during
sleeping hours. It took 2-3 hours for the temperature to
rise and stabilize. Following this period, gradual
temperature changes and abrupt fluctuations of about 0.6øC
(peak-to-peak) were observed.
Deep body temperature shows a strong circadian rhythm. It
has been suggested that this is due, at least in part, to an
endogenous variation of the thermoregulatory set point (18).
It also varies in response to a variety of behavioral and
external stimuli, including sleep (19), physical activity
(20), postural changes (21), ambient temperature (22) and
meals (23). The menstrual cycle of women also affects their
temperature rhythm, with the post-ovulatory temperature rise
increasing the overall mean (24), thus confounding
comparison of temperature rhythms recorded at different
menstrual cycle phases.
The CNS regulator of body temperature resides in the
hypothalamus, and the temperature of the hypothalamus is a
major feedback signal to the regulator (25,26). The midcycle
rise of temperature is believed to be caused by elevation of
progesterone and catecholamine levels (27).
For comparison, menopausal hot flashes are thought to be a
disorder of thermoregulation initiated centrally within the
medial preoptic area of the hypothalamus (28).The medial
preoptic area is innervated by ascending noradrenergic
neurons, and increased norepinephrine turnover in the
hypothalamus is believed responsible for the LHRH release
and the thermoregulatory changes composing menopausal hot
flashes (29,30). Peripheral circulating levels of plasma
catecholamines do not change before or during hot flashes,
but alterations in central catecholamines do occur (31-33).
Levels of plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), the
major metabolite of brain norepinephrine, are significantly
higher in women experiencing hot flashes than in those who
are not, and these levels increase further during the hot
flash itself (33). In addition, clonidine, an à2-adrenergic
agonist has been shown to reduce hot flashes and also
decrease central noradrenergic activity (34,35). Conversely,
yohimbine, an à2-adrenergic antagonist that increases
central noradrenergic activity, provokes hot flashes
(35,36).
Despite the fact that 158 years passed since Von Fricke`s
study on vaginal temperature this basal body temperature is
still probably the most widely used aid in the
identification of the ovulation day. However, it seems that
there was not much attention paid to the best hour of
temperature recording after the onset of a nocturnal sleep.
Based on recent studies it seems that 5 hours after
nocturnal sleep onset can give a better basal body
temperature recording that will more reflect the ovulatory
effects upon the other factors.
Progesterone
Increased progesterone synthesis begins before ovulation
(37,38). Yussman et al. (37) reported a preovulatory rise in
progesterone 24 to 48 hours prior to ovulation in human
subjects. Goebelsmann et al. (38) found that pregnanediol
excretion rose on the day preceding the LH and FSH peaks.
Moghissi et al. (24) confirmed that serum progesterone
begins to rise two days before the LH surge.They found that
serum progesterone rose from a level of 0.49 ñ 0.38
nanograms/ml two days before LH surge to a level of 1.16 ñ
0.92 nanograms/ml at the LH surge, and to 4.52 ñ 0.22
nanograms/ml at two days after the LH surge.
Progesterone is secreted by the adrenal cortex and accounts
for the low plasma concentrations of 1 mg/day. Luteinization
of the granulosa cells in the ovary results in additional
synthesis of progesterone during the ovulatory and luteal
phases of the menstrual cycle. Production of progesterone
reaches 25 mg/day at its peak during the midluteal phase
(39). The thermogenic effect of progesterone allows women to
utilize basal body temperatures as an indicator of ovulation
(40,41). Progesterone has been attributed with anesthetic
properties. A natural metabolite of progesterone,
allopregnanolone (3à-OH-DHP), is an effective modulator of
Cl~ flux on the ç-aminobutyric acid (GABA)/ benzodiazepine
receptor Cl~ channel complex (42), thus increasing the
effectiveness of GABA, which leads to sedation and
anxiolytic properties (43). Zuspan and Rao (44) postulated
that progesterone causes an increased excretion and
production of norepinephrine, which is responsible for the
increased thermogenesis after ovulation. They concluded that
the basic mechanism for thermogenesis is norepinephrine and
not progesterone.
Despite these facts it seems that progesterone plays a major
role in the basal body temperature rise during ovulation and
afterwards.
Sleep
Human body temperature characteristically rises during
wakefulness and falls during sleep. This daily temperature
fluctuation and the sleep-wake cycle are considered to be
rhythmic functions normally synchronized to the 24 hr solar
day. Subjects living in isolation from environmental time
cues, however, have shown temperature and sleep-wake cycles
that are almost invariably longer than 24 hr and not
necessarily synchronized to each other (45,46).
Kreider et al. (47) made simultaneous measurements of oxygen
consumption, rectal temperature and mean weighted skin
temperature on nine young men ( 32 man-nights ), who slept
at night in a "comfortable" ambient environment
(25.5-27.8øC). Significant decreases in oxygen consumption,
rectal temperature and weighted skin temperature during the
night were found. On the average, oxygen consumption
decreased gradually during the night and reached a low value
at 5.1 hours after retiring. Rectal temperature decreased
1.2øC during the night. This low point occurred 5.6 hours
after retiring and was followed by a slight but significant
elevation.
Nocturnal sleep is associated with a lowering of body
temperature. Several studies have attributed this to
negative or passive factors (48), such as absence of the
specific dynamic action of food (47,49) and muscular
relaxation (50), which would diminish metabolic activity
(47). The association of sweating with sleep suggests that
the nocturnal body temperature reduction may, in fact, be a
regulated response. In 1941, sleep-sweat studies led Day
(51) to suggest that a reduction of the thermostatic set
point occurs with sleep.
Shortly after Askerinsky and Kleitman (52) described rapid
eye movement (REM) sleep as distinct from non-rapid eye
movement sleep (NREM), Dement and Kleitman (53)
characterized the REM-NREM cycle and reported that the
duration of REM episodes progressively increased throughout
the night in normal subjects. The timing of REM sleep is
controlled, at least in part, by an endogenous circadian
oscillator which is coupled to the one generating the body
temperature cycle (54).
Many studies have demonstrated that some people naturally
have very short daily sleep requirements (55), while others
have very long sleep needs (56). Patkai et al. (57) found
that the duration of night sleep was longest during
premenses and shortest at ovulation. The actual recorded
temperature minimum in narcoleptics appeared 1 hr after
sleep onset, independent of the occurrence of sleep-onset
REM, compared with 4-5 hr after sleep onset in control
subjects (58).
Six healthy male subjects were exposed to seven different
bedtime conditions, one per week (59). Bedtimes were
scheduled in 4-hr intervals, resulting in times without
sleep ranging from 16 hr to 40 hr. Rectal temperature was
measured continuously and showed a circadian rhythm during
both sleeping and waking. A fall in temperature immediately
after sleep onset was noted at all bedtimes except at 0700
and 1900 hr. In the majority of cases temperature rose
toward the end of sleep, i.e., awakenings tended to occur
during the rising phase of the circadian temperature rhythm.
Slow wave sleep (SWS) is most heavily concentrated during
the first third of nocturnal sleep, whereas the percent of
rapid eye movement (REM) sleep gradually increases
throughout the course of nocturnal sleep, reaching a plateau
during the last third of the night (53,60).
Barrett et al. (61) examined eight adult subjects (five
males and three females), who were reportedly good sleepers.
Rectal temperature was recorded at 1-minute intervals.
Following sleep onset, body temperature dropped more rapidly
and remained lower than when wakefulness continued over the
same time, resulting in a mean sleep-evoked decrease of
0.31 ñ 0.09øC. At the sixth hour after sleep onset the body
temperature began to rise.
In conclusion, during a normal nocturnal sleep the
thermogenic circadian rhythm shows a tendency to rise at the
sixth hour after sleep onset. So, approximately at the 5th
hour after sleep onset the basal body temperature is at its
lowest level. On the day of ovulation the progesterone and
the subsequent hypothalamic norepinephrine cause the basal
body temperature to rise. This rise in the basal body
temperature at the ovulation day can be best noticed at the
lowest circadian thermogenic point, which is at the 5th hour
of the nocturnal sleep, so avoiding the masking of the BBT
by the other regulatory factors, especially its circadian
rise at awakening.
However, until more sleep studies are performed in women in
a controlled manner, it will be difficult if not impossible
to make any conclusive remarks about the appropriate time
for BBT measurement.
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