Descriptive analysis of the relationship between progesterone and basal body temperature across the menstrual cycle.

ABSTRACT

OBJECTIVE: Describe the relationship between basal body temperature (BBT) and pregnanediol-3 alpha-glucuronide (PDG, the urine metabolite of progesterone) across the menstrual cycle. DESIGN: Observational study. SETTING: Study carried out from 1996 to 1997 in eight European family planning clinics. PARTICIPANT(S) One hundred and seven normally fertile and cycling women. MAIN OUTCOME MEASURE(S) BBT and PDG level on each day of 283 cycles and ultrasound determination of the day of ovulation. RESULT: (s) In comparison with previous end-of-cycle levels, decreases in PDG and BBT on the first day of menses were seen in nearly 90% and 80% of cycles, respectively. In a non-negligible percentage of cycles, luteolysis would continue during menses between the second and the third day after menses, small but significant decreases in PDG and BBT were seen in 76% and 48% of cycles, respectively. During the peri-ovulatory phase, between the third and the second day before ovulation, PDG and BBT began to rise in 56% and 41% of cycles, respectively. There was a medium degree of correlation between PDG levels and BBT (r = 0.53; 7,279 days with available measurements). The relationship between PDG levels and BBT was linear at low PDG levels but BBT increased no longer when PDG levels continued to rise above a threshold of nearly 10 mcg/mg Cr. CONCLUSION: (s) PDG and BBT had parallel increases at low PDG rates but diverged at higher rates.