The allopregnanolone to progesterone ratio across the menstrual cycle and in menopause

•The allopregnanolone/progesterone ratio decreases 8-fold across the menstrual cycle.•Allopregnanolone and progesterone levels are very low in menopause.•The ratio is lower in the luteal phase than even in postmenopausal women.•These data may have implications for luteal phase mood disorders. The neuroactive steroid 3α-5α-tetrahydroprogesterone (allopregnanolone), a metabolite of progesterone, is a positive allosteric modulator of GABAA receptors, and low levels have been implicated in the etiology of mood disorders. However, it is not known whether metabolism of progesterone to allopregnanolone varies across the menstrual cycle or is low after menopause. We hypothesized that the allopregnanolone/progesterone ratio would decrease from the follicular to luteal phase. We also hypothesized that postmenopausal women would have lower levels of progesterone and allopregnanolone but similar allopregnanolone/progesterone ratios as premenopausal women in the follicular phase. Serum fasting allopregnanolone and progesterone levels were measured by gas chromatography-mass spectrometry in ten premenopausal women at the follicular, mid-cycle, and luteal phases of the menstrual cycle and in twenty-four postmenopausal women. Although allopregnanolone and progesterone levels increased from the follicular to luteal phase, the allopregnanolone/progesterone ratio decreased 8-fold [0.33 ± 0.08 (follicular) vs 0.16 ± 0.09 (mid-cycle) vs 0.04 ± 0.007 (luteal), p = 0.0003]. Mean allopregnanolone and progesterone levels were lower in postmenopausal than premenopausal women at all menstrual cycle phases (p