In IVF, the hCG trigger is used to trigger final egg maturation so the eggs can be retrieved and fertilized. The trigger is meant to mimic the natural luteinizing hormone (LH) surge that initiates ovulation during the menstrual cycle. However, hCG can sometimes cause excessive reactions, leading to a potentially dangerous condition known as ovarian hyperstimulation syndrome (OHSS).
To reduce the risk of OHSS, GnRH agonist triggers have been used to induce an LH surge that mimics the natural LH surge in the body. However, GnRH agonists cause a shorter LH surge that can result in corpus luteum defects, resulting in lower pregnancy rates and higher miscarriages during fresh transfers (Humaidan et al. 2015).
This led to the development of new triggering methods for fresh transfers, such as the dual trigger and double trigger. Both methods combine a GnRH agonist with low-dose hCG, but the double trigger administers the two shots at separate times. These strategies help lower OHSS risks without compromising the corpus luteum.