Gonadotropin-releasing hormone agonist (GnRH-a) has been used to suppress gonadotropins in 
several conditions including endometriosis, uterine fibroids, central gonadotropin- dependent 
precocious puberty, where gonadotropin suppression does not occur immediately, but there is a 
transient increase “flare" in sex hormone levels, followed by a lasting suppression of hormone 
synthesis and secretion. When using GnRH analogues to trigger ovulation, the mean concentration of 
LH as measured by radioimmunoassay may be actually raised although there is reduced pulsatile 
secretion and so the bioactive LH is markedly reduced, where the GnRH-a induced surge consists of 
two phases; a short ascending one (4h) and a long descending one (20 h), with subsequent induction 
of an FSH surge comparable with the surge of the natural cycle.