Hormonal profile of the cycle in 68 normally menstruating women

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Abstract
: The peripheral plasma levels of immunoreactive LH, FSH, oestradiol and progesterone were analyzed daily throughout the cycle in 68 normally menstruating women, exhibiting a cycle length of 25 to 36 days during the period of blood sampling. The (geometric) mean length of the follicular phase was 15 days, with an individual variation between 9 and 23 days. The mean length of the luteal phase was 13 days, with an individual variation between 8 and 17 days. The mean ratio of the length of the follicular to luteal phase (F/L ratio) was 1.13, and 62 of 68 subjects (91%) exhibited an F/L ratio between 0.75 and 1.80. In one-third of the cycles studied. the pre-ovulatory oestradiol and LH peaks occurred before the 12th, or after the 18th day of the cycle, and the length of the luteal phase was shorter than 12, or longer than 15 days. The length of the follicular phase was positively correlated to the mean LH level of days LH-7 to LH-3 before the midcycle surge (P< 0.001) and negatively correlated to the mean oestradiol level of the first 6 days of the cycle (P< 0.001) and to the height of the preovulatory oestradiol peak (PP< 0.01) or during days LH-7 to LH-3 (P < 0.001), or the height of the midcycle LH surge (PP < 0.001), or of the entire follicular phase (P < 0.001), or of the complete cycle (P < 0.01). Hence a combination of high initial oestradiol levels with low LH levels is associated with relatively short cycles and the opposite combination with relatively long ones. In agreement with previous findings in 32 normally menstruating women, 94%, or 64 of the 68 subjects of the present study had plasma progesterone levels higher than 16 nmol/1 for a minimum of 5 days. Hence, progesterone levels lower than this value or exceeding this value for a shorter period than 5 days are considered to reflect an insufficient or partially suppressed luteal function. In addition, 62 of the 68 subjects studied (91%) fulfilled a series of criteria concerning the minimal and maximal levels of LH, FSH, oestradiol and also progesterone during different cycle phases. It is suggested that these criteria together with the progesterone levels indicated above are characteristic of a normal ovulatory cycle, at least in the local population. The acquisition of similar 'critical levels' in other populations may provide a useful approach towards the establishment of generally accepted criteria for distinguishing a normal from an abnormal cycle.