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Reliability of bbt in fertility investigation
European Journal of Obstetrics & Gynecology and Reproductive Biology, 47 (1992) 121-127 992, Accepted for publication 13 August 1992.
The reliability, acceptability and applications of basal body temperature (BBT)
records in the diagnosis and treatment of infertility.
Antonio R. Martinez, Marcel H.A van Hooff, Erik Schoute, Maartje van der Meer,
Frank J.M. Broekmans and Peter G.A. Hompes
Division of Reproduclire Endocrinology and Fertility, Department of Obsterics and
Gynecology, Free University Hospital, Amsterdam, The Netherlands.
The possibilities and limitations of basal body temperature (BBT) records as an
adjunct in the management of infertility were re-evaluated. To assess its accuracy as
an index of ovulation, 172 charts were analyzed by three different physicians. While
the average true positive rate was 90%, the false negative rate was only 2%. The
remaining graphs (8%) were classified as non-interpretable, probably reflecting
measurement problems. Retrospective assessment of 210 biphasic records showed the
thermal nadir to occur within I day of the urinary luteinizing hormone (LH) surge in
75% of the cases, and in 90% when 2 days where considered. This confirms BBT as a
relatively accurate guide for retrospective identification of the pericivulatory period.
Moreover, results of a study conducted to investigate how patients experienced daily
recording of BBT graphs suggest that the method is well accepted by a high
proportion of women. From all these it appears that there are many indications where
BBT graphs can still be applied. Development of new electronic devices may further
improve the reliability, acceptability and applications of the BBT records in the
Basal body temperature; LH test; Infertility; Ovulation
The observation that the basal body temperature (BBT) has a biphasic pattern during
the menstrual cycle was first reported by William S.
Correspondence to. Marcel H.A. van Hooff, M.D., Division Reproductive
Endocrinology and Fertility, Department Obsterics and Gynecology, Free University
Hospital, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands.
Squire in 1868 in the transactions of the London Obstetrical Society . Mary Putnam
Jacobi, one of the first American woman physicians, also noticed the biphasic curve
of the basal temperature in women (21, but they both failed to connect this finding to
ovulation. A possible relationship between the timing of evaluation and the shift in the
BBT was first suggested in 1904 by the Dutch gynecologist Theodoor Hendrik van de
Velde  Later in 1926, he clarified that the corpus luteum was responsible for higher
temperatures in the second half of the cycle and that the end of corpus luteum activity
caused menstruation. He also clearly stated that the temperature shift was related to
ovulation [4). Since that time there has been good evidence for the clinical use of the
BBT graph [5-8] and it has been widely applied as a simple, inexpensive method to
determine whether ovulation has occurred and to estimate its timing in the menstrual
cycle. However, often more has been expected from the BBT graph, both in
concurrent and retrospective interpretation, than it can actually provide. As a
consequence, its value has been questioned and uncertainty has emerged with regard
to the concrete possibilities and applications of the BBT chart. Moreover, the recent
development of new methods and techniques allowing a more accurate prediction and
detection of ovulation has raised questions on the current place of the BBT record in
the diagnosis and treatment of infertility problems.
The present study is intended to re-assess the reliability of the method as well as its
possibilities and limitations in fertility investigation. In addition, the acceptability by
the patients and their personal experience with the performance of BBT charts were
evaluated. The applicability of the method and the potential role that novel
computerized measuring devices may play in this area is further discussed.
Reliability of BBT records
Detection of ovulation
Basically, a BBT record provides information on the existence of either a biphasic or
a monophasic pattern. A biphasic BBT graph is assumed to be indicative of ovulation
and reflects the central effect of increasing plasma progesterone levels secreted by a
functional corpus luteurn . However, ovulation has been reported to occur in 3% to
20% of monophasic BBTs when based on hormonal or sonographic criteria 18-121.
Another study  found that when using the occurrence of pregnancy as ovulation
criteria, all charts studied (n = 110) showed a biphasic BBT pattern. On the other hand,
the chance that biphasic BBTs could be observed during an ovulatory cycles is almost
nihil [8,121. These data suggest that the method has in fact a high specificity, defined
as the ability to identify the true-negatives, whereas the sensitivity, the ability to
identify true-positives, has been found variable according to the different studies.
The accuracy in identification of a BBT pattern is mainly affected by factors related to
the method itself, and by the interpretation of the observer. Factors related to the
method include either improper recording, illness, diet, medication and sleeping
pattern alterations, or inability of an adequate level of progesterone to exert its
thermogenic effect. Correct interpretation of a record has been commonly associated
to the knowledge and experience of the observer.
Most of the published studies evaluating the reliability of BBT graphs as a method of
ovulation detection have expressed their results in terms of monophasic or biphasic
patterns. However, such a differentiation is in fact not always very clear, particularly
To investigate to which extent the occurrence of poorly defined or erratic patterns
could affect the accuracy of BBT readings as an index of ovulation, 172 charts from
54 normally cycling women (mean 3.2, SD ± 1.7, range 1-6 charts per woman) were
independently analyzed by three different physicians. They were unaware of the
patients medical history and were asked to quailify the records as either biphasic,
monophasic or non-interpretable, according to their own interpretation criteria. One
hundred and twelve of the cycle's (65%) were spontaneous, whereas 60 cycles (35%)
were stimulated with 100 mg clomiphene citrate (CC) (Serophene, Scrono, Geneva,
Switzerland) daily from days 3 to 8 of the cycle. All cycles were ovulatory as
confirmed by daily vaginal ultrasound monitoring . The three physicians
participating in the study worked in our Division of Reproductive Endocrinology and
Fertility and had different grades of experience with the interpretation of BBT charts.
Observer A was a recently initiated fellow, observer B was an experienced
gynecologist, and observer C was an advanced resident in obstetrics and gynecology.
* Biphasic * Non-interp. * Monophasic
Fig. 1. Percentage of BBT graphs (n - 172) qualified as biphasic, non-interpretable or
monophasic by three different ob- servers.
The obtained results are shown in Fig. 1. The number of records identified as biphasic
were 170 (98.8%) for observer A, 157 (91.3%) for observer B, and 140 (81.4%) for
observer C, giving an average true positive rate of 90.5%. There were 2 charts marked
as monophasic by observer B, and 5 by observer C, which represents a false negative
rate of 1.3% and 2.9%, respectively. The remaining 2 (1.3%), 13 (7.5%) and 27
(15.7%) charts were qualified as non interpretable by the respective observers. There
were no substantial differences observed in the interpretation of records from either
The rate of true-positive findings observed in this study coincides with data in the
literature [8,10,12] and reconfirms the discrepancy between investigators concerning
the interpretation of BBT charts. However, in this study such discrepancies were
found to be mainly based on the number of charts considered as non-interpretable.
The observation of these irregular patterns, which may probably reflect methodologic
and/or technical problems rather than the occurrence of definite monophasic records,
seems to be the major cause of erroneous interpretations and could explain the
discrepancies between studies. The strength of the criteria used to define a biphasic
pattern appeared to be associated with the experience of the observer. The low
percentage (2%) of clear false-negative patterns found in this study contributes to
validate the accuracy of BBT graphs as an index of ovulation. Moreover, these
findings suggest that the incidence of noninterpretable records could be substantially
reduced not only by improving aspects related to the interpretation criteria but
following a refinement of the measurement techniqe .
Fig. 2. Time relationship between the day of urinary LH surge detection (day 0) and
the day of the BBT nadir in sponta- neous (n = 94) and clormiphene citrale (n = 116)
The anticipation of ovulation using a concurrent BBT graph has long been used as an
aid to conception and for timing of insemination. The two most common suggestions
for the BBT graph as a concurrent method of predicting ovulation are a dip (nadir) in
the curve, that signals the approach of ovulation, and a subsequent sharp rise between
two successive days indicating ovulation. Although it is now well accepted that the
BBT graph is an unreliable marker for the prediction of ovulation , it still could be
useful as a simple method for retrospective identification of the presumptive day of
ovulation. Among the numerous parameters used to detect the day of ovulation, the
identification of the luteinizing hormone (LH) surge appears to be the most reliable
indicator of impending ovulation [171. The relationship between the thermal nadir
and the LH surge have been stressed by different studies in the past [18-201. In order
to asses the accuracy of BBTs in retrospectively predicting the day of the Urinary LH
surge, we analyzed 210 records of 88 patients (mean 1.8, SD ± 0.7, range 1-4 cycles
per patient) who underwent intrauterine insemination with their husbands' semen.
Ninety-four (45%) cycles were spontaneous and 116 cycles (55%) were stimulated
with 100 mg CC (Serophene, Serono) daily from days 3 to 8 of the cycle. Monitoring
of an LH surge was performed in morning and evening urine samples by means of the
LH Color' test (Organon, Oss, The Netherlands), which detects the LH peak on
average 16 to 28 hours before ovulation. The characteristics of the test as well as its
clinical Teliability for the prediction of the time of ovulation have been previously
reported . All cycles included in the study had presented a positive test,
presumably reflecting the occurrence of a urinary LH surge above 50 U/l, and were
ovulatory as confirmed by daily vaginal ultrasound [15). A reproductive
endocrinologist, experienced in the reading of BBTs and having no prior knowledge
of patients' results, was asked to review the charts and to predict retrospectively the
day of the LB surge by determining the thermal nadir (subjective interpretation). The
day of urinary LH Surge detection was considered as day 0, and the number of cycles
where the nadir differed around the LH surge were expressed as cumulative
The results obtained from this study are shown in Fig. 2. There were no differences in
the relationship of thermal nadir to urinary LH surge between spontaneous and CC
stimulated cycles. From all cycles, in 66 cases (31.5%) the LH surge occurred on the
day of the nadir, in 157 cases (74.8%) when ± I day was considered, and in 193 cases
(91.8%) the nadir was found within ±2 days of the LH surge. For the remaining cases
the surge fell more than 2 days from the nadir.
These findings closely coincide with other published studies relating the BBT nadir to
the day of the LH surge [18-201 and reconfirms the inaccuracy of BBT records for the
prediction of ovulation. However, when retrospectively analyzed, in 75% of the cases
the thermal nadir was noted within I day of the LB surge and in more than 90% of the
cases when 2 days where considered. This indicates that BBT charts still can provide
a reasonably accurate guide for retrospective assessment of events related to the
Despite the extensive use of BBT graphs in clinical practice, and the active
participation it demands from the patients, not much attention has been payed to the
customers concern with the method in most of the reported studies. The following
study was conducted to investigate how women experienced daily recording of HBT
graphs and the factors which could affect their qualification of the procedure.
The first 100 patients who, from the start of the study, attended our Division of
Reproductive Endocrinology and Fertility, were given a standard questionaire. The
answers were returned anonimously and always on a voluntary basis. The first
questions were related to demographic data, education, kind of work and reason of
consult. Patients were asked for the number of cycles they had kept a BBT chart (=<
3,4-6, => 7) and whether it was related to: (a) the fertility investigation, (b)
monitoring of a treatment or, (c) voluntary use as a method of self-observation. To
qualify the burden associated to the performance of the method four possible
alternatives were offered: (a) very burdensome, (b) burdensome, W little burden, or
W no burden. Finally, patients were asked whether they considered to keep BBT
records as a part of their treatment and/or investigation as either: (a) a positive
experience, (b) a negative experience, or W indifferent.
Eighty-one out of the 100 distributed questionaires were returned. All patients but one
had previous experience with keeping BBTs, and these were included in further
analysis. Mean age of the patients was 31.4 years (SD ± 4) ranging between 25 and 43
years. Regarding education 3 (4%) had only completed primary school, 40 (50%) had
completed high school, and 37 (46%) had received higher education. AS related to the
work situation in 2 cases the answers were equivocal, 37 patients (47%) worked more
than 20 hours a week, 21 patients (27%) worked 20 hours or less, and the remaining
The reason for consulting was infertility in 74 cases (92.5%), other reasons in 3, and
not known in another 3 cases. From the total group 69 patients (96%) were currently
keeping a BBT chart or had done so within the last year, whereas 11 (14%) stopped
recording more than I year ago. The number of cycles that patients had kept a BBT
chart according to the indications is given in Fig. 3. In a majority of the cases (54.5%)
the indication was related to the fertility investigation, in 35 cases (29%) it was used
for monitoring of a treatment, and in 20 cases (16.5%) it was done just as a method of
self-observation. In almost half of the cases BBTs had been kept for more than 6
cycles. Most of the patients (95%) recorded rectal temperature, 2 patients did it
Regarding the burden associated with the procedure, it was qualified as very
burdensome by 10 patients (12%), burdensome by 23 (29%), as a little burden by 35
(44%) and as no burden by 12 (15%). When asked about their personal experience
with the method, 6 patients (7.5%) expressed it was for them a negative experience,
37 patients (46%) considered as positive the experience of keeping the BBTs during
their investigation, and for 37 patients (46%) it was indifferent. Factors such as age of
the patients, education or the category of infertility did not substantially affect either
the degree of burden associated with the procedure or the way the patients
experienced the method. However, when considering the patients' occupational
situation, it was found that a remarkably higher proportion (73%) of patients working
more than 20 hours a week had expressed small or no burden associated with the
performance of the method as compared to the groups working 20 hours or less
(47.5%) or without an active job (40%), (XI test: P < 0.05). When associating the
burden of the procedure with the experience of the method (Fig. 4), it was found that
while most patients with a negative experience considered the method burdensome (5
out of 6), still 10 (30%) of the patients who regarded the procedure as burdensome
expressed to have a positive experience with the method.
These findings suggest that, despite the intensive participation required, the use of
BBT records is a well accepted method by a high proportion of our patients
population. The active involvement in the investigation and/or treatment of their
fertility problems as well as the awareness of their own biological changes are
speculative reasons that could account for this. Whether user acceptability might
further be improved with the advent of novel and more practical measuring devices
Fig. 4. Percentage of patients expressing a negative, indifferent or positive experience
with the method as associated to the related burden (B + VB: burdensome to very
The BBT offers the advantage of being a simple, cost-effective and reliable method
for retrospective timing and identification of the occurrence of mutation. Its
possibilities and limitations well understood, the BBT may still be used as a valuable
auxilliary too] in the diagnosis and treatment of infertility problems. The BBT serves
Several functions: (1) gives a rapid and objective impression about the length of the
cycle, possible occurrence of ovulation, and the characteristics of the menstrual
pattern; (2) indicates frequency and timing of sexual intercourse; (3) provides
information for scheduling of post-coital tests and cervical factor evaluation. By this
means a great proportion of normal cases can be easily evaluated, while considering
the use of more sophisticated techniques only for cases with doubtful or negative
results; (4) evidences the occurrence of a short luteal phase (< 11 days) and helps in
planning of endometrial biopsies; (5) aids in timing and interpretation of hormonal
determinations; and (6) monitors the effect of ovulation -inducing agents.
Besides its applications in the diagnosis and treatment of infertility, BBT records have
been extensively used as an important element of family planning practice. For this
purpose, new sophisticated digital-electronic BBT recording devices have been
developed in an effort to simplify and improve these measurements [22). Most of
them are oral thermometers that utilize microcomputcr-assisted repeated calculations
giving information on a liquid crystal display in only a few seconds. These devices
document BBT measurements in a built-in computer program- Algorithms are
incorporated that indicate the fertile and non-fertile phase of the cycle, whether
ovulation has been occurring, and the expected more fertile phase of the current cycle.
Some devices also allow the possibility of printing out previously recorded readings.
One of the most sophisticated devices available is the Baby Comp (Valley Electronics,
Eschenlohe, Germany), which possesses an 8-bit micro-processor, with 128
computational registers, and the possibility to store information of up to 48 cycles (4
years). It is also programmed to recognize operational errors. In case of unusually
marked temperature variations or skipped measurements, the device automatically
calculates the missing readings and these will not be used in the evaluation. By
pushing a button information is incorporated on whether or not the patient is
menstruating. The possibility that a conception has occurred is displayed after 10-18
days, and calculation of the delivery date is based on the probable day of conception.
The possibility to modify these devices to process information related to parameters
that can be used by the clinicians in the diagnosis and treatment of infertility would
still further improve the reliability of BBT measurements, its acceptability by the
patients as well as their clinical applications.
The BBT graph has largely been used as an important adjunct in the fertility
investigation. The main advantages associated to this method have been its simplicity,
noninvasiveness and low cost. In the last years, with the advent of more sophisticated
methodologies, its value has been questioned and doubts on its current place have
arisen. In the present study the reliability and applicability of BBT records was
reevaluated in. the actual context of new fertility management techniques.
The method showed a high sensitivity when used as an index of ovulation. This was
in agreement with previous studies. From our investigation, however, it appears to be
the occurrence of irregular records, here classified as non-interpretable, the main
contribution to erroneous results. Future refinements in the recording and
measurement techniques might further improve the accuracy of the BBT graph for the
detection of ovulation. The unreliability of BBT records for the prediction of
impending ovulation, as compared to rapid urinary LH surge detection, was
reconfirmed. In addition, it was demonstrated that it still can provide a reliable guide
when used for retrospective identification of the presumptive day of ovulation.
The way patients experienced daily keeping BBT records and their reliance on the
method has, to our knowledge, not been previously reported. This pilot study, which
was representative of our patient population, clearly suggests that the method is well
accepted by a majority of the women. Although 41% found the procedure
burdensome, only 7.5% of the patients reported a negative experience with the
These findings indicate that there are many indications, in the study and management
of fertility problems, where the BBT graph can still be applied. Moreover, it is to be
expected that the development of new electronic devices allowing the incorporation of
relevant fertility data will further improve the reliability, acceptability and
applications of BBT records in the fertility investigation.
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