The availability of gonadotropin releasing hormone (GnRH) antagonists did not only offer clinicians an alternative to GnRH agonists but, more importantly, has led to the development of new concepts aiming to increase safety and simplicity in ovarian stimulation. These include the modified natural cycle, mild in vitro fertilization (IVF), the use of GnRH agonist for triggering of final oocyte maturation with elective cryopreservation in patients at risk of developing ovarian hyperstimulation syndrome (OHSS), the administration of antagonists during the luteal phase for management of severe OHSS, as well as control of endogenous luteinizing hormone (LH) with GnRH antagonists in intrauterine insemination (IUI) cycles. Administration of GnRH antagonists can be performed by either a single dose or by using a daily scheme. The need to simplify ovarian stimulation led to the development of long-acting follicle stimulating hormone (FSH).

Survival rates after cancer have increased significantly in recent decades; however, these treatments also have drawbacks and patients (or parents in the case of children) must be informed of the long-term side effects of oncological treatments and the possible options for preserving the fertility of these patients. In oncological patients two special circumstances often arise: a short time to stimulate ovulation and the necessity of not reaching high estradiol levels. In applying embryo-freezing techniques to preserve the fertility of oncology patients, it is very important to know the couple's preference for the disposition of any unused embryos. Up to now, embryo cryopreservation has been the only clinically accepted method for preserving the fertility of oncology patients before they undergo chemotherapy and/or radiotherapy. The post-thawing pregnancy rates are acceptable and are around 30% per cryoreplacement depending on the number of embryos available and their quality.