Objective: To assess whether temperature is increased by medroxyprogesterone (MPA) and thus whether basal temperature records could be used to determine ovulation during cyclic MPA therapy.
Design: A 2-month double-blind placebo-controlled crossover trial in which oral basal temperature was measured daily.
Setting: Normal human volunteers in an academic medical environment.
Subjects: Eleven postmenopausal women not taking gonadal hormones.
Intervention: Medroxyprogesterone acetate (10 mg/d) or placebo, calendar days 16 to 25, with crossover.
Main outcome measures: Comparison of mean temperature days 17 to 26 during MPA versus placebo; comparison of differences between temperatures days 7 to 16 and 17 to 26 in MPA versus placebo months; and analysis for a significant monthly thermal shift.
Results: The mean temperatures during MPA treatment averaged 0.27 degrees C higher than during the placebo phase and showed a significant change from pretreatment to "treatment" phases during MPA but not during placebo cycles. Eight of the MPA and one of the placebo cycles showed a shift from lower to higher temperatures days 16 to 25.
Conclusions: Medroxyprogesterone acetate has a physiological progesterone-like thermal effect. Therefore basal temperature data cannot reliably indicate ovulation during cyclic MPA administration.