of ovarian follicles of at least 15 mm, and serum estradiol level of 0.49 nmol/L before commencing final maturation induction. There are better prospects at a follicle size of 18 mm and serum estradiol level of 0.91 nmol/L. Medications Medications used for final maturation and/or release of oocytes include: Human chorionic gonadotropin (HCG or hCG) in a low dose, which may be injected after completed ovarian stimulation. Final maturation with hCG is also termed hCG priming. Ovulation will occur between 38 and 40 hours after a single HCG injection. It is also used in in vitro fertilization, where it makes the follicles perform their final maturation. A transvaginal oocyte retrieval is then performed at a time usually between 34 and 36 hours after hCG injection, that is, shortly before when the follicles would rupture. A retrieval at 36 hours after final maturation induction appears to result in optimal embryo quality and pregnancy outcomes. HCG injection confers a risk of ovarian hyperstimulation syndrome. Recombinant luteinizing hormone (rLH), recombinant HCG (rHCG) and urine-derived hCG (uHCG) are equally effective in achieving final follicular maturation in IVF with regards to pregnancy rates and risk of ovarian hyperstimulation syndrome. Therefore, urine-derived hCG (uHCG) is regarded as the best choice for final oocyte maturation triggering in IVF due to availability and cost. GnRH agonist, which necessitates using a GnRH antagonist protocol for suppression of ovulation during ovarian hyperstimulation, because using GnRH agonist for that purpose as well inactivates the axis for which it is intended to work for final maturation induction. HCG versus GnRH agonist Final maturation induction using GnRH agonist results in a substantial decrease in the risk of ovarian hyperstimulation syndrome (OHSS). A Cochrane review estimated that using GnRH agonist instead of hCG in IVF decreases the risk of mild, moderate or severe OHSS with an odds ratio of approximately 0.15. The review estimated that, for a woman with a 5% risk of mild, moderate or severe OHSS with the use of HCG, the risk of OHSS with the use of a GnRH agonist would be between 0 and 2%. However, using GnRH agonist has a lower live birth rate than when using hCG in autologous oocyte transfers (rather than ones using oocyte donation). A Cochrane review of autologous oocyte transfers estimated that GnRH agonist, compared to hCG, gives an odds ratio of pregnancy of approximately 0.47. It estimated that, for a woman with