When Is The Right Time to Trigger With Clomiphene?

It is common practice to trigger ovulation at 18 mm size follicle.  Surprisingly all this has been standardised, and all the evidence which has been obtained has been obtained on the basis of studies done in the 1980s and 1990s, however many of the studies were done on those of IVF rather than on Clomiphene or Letrozole.

In an analysis of 988 cycles published in Fertility and Sterility, in a retrospective analysis they looked at the best time to trigger ovulation, rather than triggering at 18 mm; triggering at 22 and 23 mm seemed to give the best chance of success as well as improving the endometrial lining. By waiting for the follicles to grow larger, the endometrial thickness varied and improved, thus it may be important to wait and trigger ovulation around a slightly later time so as to improve the chances of pregnancy.