In Vitro Fertilisation (IVF)
An assisted reproduction technique where eggs are fertilised with sperm in a laboratory, and resulting embryos are transferred to the uterus. GnRH antagonists (cetrorelix, ganirelix) are routinely used during IVF to prevent premature ovulation, enabling controlled egg retrieval.
Technical Context
IVF protocol stages: (1) controlled ovarian stimulation (COS — exogenous FSH ± LH for 8-14 days to develop multiple follicles; GnRH agonist or antagonist prevents premature ovulation), (2) trigger (hCG or GnRH agonist injection when lead follicles reach 17-18mm — initiating final oocyte maturation), (3) oocyte retrieval (transvaginal ultrasound-guided aspiration 34-36 hours after trigger), (4) fertilisation (conventional IVF or ICSI), (5) embryo culture (to day 3 cleavage stage or day 5 blastocyst), (6) embryo transfer (fresh or frozen-thawed), and (7) luteal phase support (progesterone ± oestrogen to support implantation). GnRH antagonist protocol advantages: shorter stimulation, no flare effect, lower OHSS risk (especially with GnRH agonist trigger), and flexibility in cycle start timing. GnRH agonist long protocol: provides more complete pituitary suppression but requires 2-3 weeks of down-regulation before stimulation begins.