An Updated Basal Body Temperature Method Erica Frank* and Randall Whitet

Basal body temperature (BBTJ readings are handicapped as fertility predictors by exogenous influences on women?s temperatures, many of which could be adjusted for by the

presence of a non-cycling control. We, a married, co- habiting couple, tracked our BBTs for two months. We found substantial temperature covariability. When there were difficult-to-explain changes in the female partner’s temperature, similar changes in the male partner’s tem- perature suggested that these fluctuations were not attrib- utable to ovulation. Additionally, a clear mid-cycle wid- ening of our temperature gap suggested that ovulation had occurred. This is a limited trial of a new method. However,

the potential for substantially improving the accuracy and usefulness of a globally utilized method, coupled with its inexpensiveness, ease, and painlessness, call for a larger study. 0 1996 Elsevier Science Inc. All rights reserved. CONTRACEPTION 1996;54:319-321

KEY WORDS: contraception, family planning, infertility, basal body temperature

Introduction

T racking basal body temperatures (BBTs) is a method used by many couples trying to con- ceive or to avoid conception. Yet there are a

number of difficulties with accurately determining the timing of ovulation using this method. 1,2 A num- ber of factors other than hormonal changes can affect a woman’s BBT, including exact time of day at which temperatures are taken, amount of sleep and sleep disturbances, ambient bedroom temperatures and convection currents, and various activities, both vol- untary (such as food ingestion) and involuntary (such as emotional responses).‘-5

Ideally, one could adjust for these exogenous influ- ences on BBT by enlisting a control subject for the

‘Emory University School of Medicine, Dept. of Family and Preventive Medicine, Dept. of Medicine, Atlanta, GA; and tHuman and Natural Ecology Program, Emory University, Atlanta, GA, USA

Name and address for correspondence: Erica Frank, M.D., M.P.H., Emory University Schoool of Medicine, Department of Family and Preventive Medicine, 69 Butler St., SE, Atlanta, GA, USA 30303-3219. Tel, (404) 616-5603; Fax: (404) 616-6847

Submitted for publication June 24, 1996 Revised July 30, 1996 Accepted for publication July 30, 1996

0 1996 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010

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woman. This control would have similar exogenous influences, but no hormonal changes. For many BBT- using couples, such a control exists: the woman’s partner.

Materials and Methods We tracked BBT for ourselves (a married, co-habiting couple not using hormonal contraceptives) for five months, using methods recommended by the BBT thermometer package insert. For both subjects, tem- perature was taken using the same BBT thermometer, shaken down to <96.0°F before each reading. Readings were taken on first awakening for each subject, within 3 min of the other, for a period of 4 min. We varied whose BBT reading was first taken.

Results As can be seen in Figures 1-5, there was considerable temperature covariability, with fluctuation in EF’s temperatures usually closely echoed by changes in RFW’s temperatures. There was also (Table 1) an en- larged post-ovulatory gap between EF’s and RFW’s temperatures. LH surges were determined by positive readings on home urinary LH test kits. A follicular phase progesterone level (23 ng/dl, normal = ~50 ng/ dl) was recorded at the Emory University endocrinol- ogy laboratory on day 15, and a luteal phase proges- terone (950 ng/dl, normal = 30-2500 ng/dl) was recorded on day 30 of the first cycle.

Discussion This new method for improving the accuracy of BBT use by standardizing BBTs to a non-cycling control

Table 1. Mean and median pre- and post-ovulatory tem- perature gaps

Pre-ovulatory Gap Post-ovulatory Gap

Mean Median Mean Median

Total 0.2 0.2 0.6 0.6 Month #1 0.1 0.1 0.7 0.6 Month #2 0.3 0.3 0.7 0.6 Month #3 0.2 0.2 0.7 0.7 Month #4 0.2 0.2 0.5 0.4 Month #5 0.2 0.2 0.6 0.6

ISSN OOIO-7824/96/$15.00 PI I SO01 O-7824(96)001 87-4

320 Frank and White Contraception 1996;54:319-321

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Contraception 1996;54:319-321

An Updated BBT Method 321

has many potential advantages. It is free, convenient, painless, and provides another way to integrate the male partner into the family planning process. This method could be used to diminish the effect of non- hormonal confounders of women’s BBTs by adjusting women’s BBT readings for changes in male partners’ temperatures. With the knowledge of RFW’s tempera- tures, EF’s preovulatory temperature dips and rises are more easily interpreted as exogenously influ- enced, since RFW’s temperature usually likewise changed. EF’s temperature elevations at the time of ovulation, however, were not paralleled. The mean and median post-ovulatory temperature gap was three times the size of the pre-ovulatory gap, and this change in gap size occurred soon after ovulation and was maintained, providing an immediate, inexpen- sive indication that the cycle had begun its luteal phase.

Having a non-cycling control could decrease errors in estimating the magnitude and direction of effects of exogenous influences on womens’ BBT, and could decrease the need to wait for retrospective (end of cycle) analysis of BBT changes. This could help sci- entifically unsophisticated or poor couples (without easy access to urinary LH or progesterone testing) around the world to discriminate between random fluctuations and the temperature increase of the lu- teal phase.

Assessments of the method’s accuracy are limited by our sample size of only one couple and only five cycles, but this small sample of correspondences sug- gests that this could be a useful method. Our initial demonstration of usefulness, as well as the method’s other attractions, suggests that a larger study would be appropriate.

Acknowledgment We wish to acknowledge Nathaniel Etheridge Frank- White, without whose inspiration this investigation would not have been conducted.

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References DeMouzon 1, Testart T, Lefevre B. Pouly J, Frydman R. Time relatidnships between basalbody temperature and ovulation or plasma progestins. J Reprod Med 1984;41: 254-9. McCarthy JJ, Rockette HE. Prediction of ovulation with basal body temperature. J Reprod Med 1986;31:742-7. West JB. Best and Taylor’s physiological basis of medical practice, 12th ed. Philadelphia, PA:WB Saunders Com- pany, 1991. Guyton AC. Textbook of medical physiology, 8th ed. Philadelphia, PA:WB Saunders Company, 199 1. Ganong WF. Review of medical physiology, 15th ed. Norwalk, CT:Appleton and Lange, 199 1.