The effect of dydrogesterone on the mid-cycle gonadotrophin surge in regularly cycling women

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