Ovulation is triggered mainly by two types of medications; HCG, which is available as Ovidrel, Gonasi or Pregnyl and Suprecur which is an analogue trigger. Both triggers act in different ways. The HCG trigger mimics the LH hormone (the hormone that starts the process of ovulation). When we look at the efficacy of this, often in IVF, we use an analogue trigger to lower the incidence of ovarian hyperstimulation syndrome. Though when we use this trigger, we know that freezing of embryos gives us a much better pregnancy rate, while using HCG gives a much better pregnancy rate during a fresh cycle.
Often it is asked, what if we give this during an intrauterine insemination cycle and use a Suprecur trigger when a woman gets more than three or four follicles? A study published in Fertility and Sterility in 2017 looked at randomising women who were given the analogue trigger which is Suprecur, and doing IUI along with an HCG trigger, and what that demonstrated is that even when nature was used to its best by doing IUI, with an HCG trigger the pregnancy rates rose to a significant 32 per cent, while it dramatically dropped to less than ten per cent in an agonist trigger. Thus there is good evidence now coming up in cases of stimulation of the ovaries in an intrauterine insemination cycle, where it is better to have a low stimulation, getting between one and three follicles and to use an HCG trigger.