THE EFFECT OF DYDROGESTERONE ON THE MID‐CYCLE GONADOTROPHIN SURGE IN REGULARLY CYCLING WOMEN

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Abstract
The effect of dydrogesterone, a retro-progesterone on the spontaneous mid-cycle surge of gonadotropin in regularly cycling women, was investigated. Blood samples were collected through 2 complete cycles in 6 subjects. The 1st untreated cycle acted as a control for the 2nd cycle during which dydrogesterone (10 mg twice daily) was administered. The start of treatment ranged from day 1 (1 subject), mid follicular phase (3 subjects) to post-ovulation (2 subjects). In all subjects where dydrogesterone was given before ovulation, the mid-cycle gonadotropin surge was either abolished or markedly diminished. Despite this follicular growth occurred in all 4 subjects and subsequently luteinization was observed in 3. Dydrogesterone given after ovulation did not produce any alteration in endocrine profiles but menses was postponed in both subjects. Dydrogesterone can mimic the known blocking actions of progesterone on the mid-cycle gonadotropin surge and can support a secretory endometrium for a limited period in the absence of endogenous progesterone.