To increase efficiency of IVF methods, we aim at obtaining more than one woman’s ova (wherever this is feasible or not contra-indicated) and this is because: one or more of the ova may not be fertilized in vitro, or some of the fertilized ova may not continue their development; we wish to transfer embryos of best quality and therefore we want to have selection choices at the stage of embryotransfer; we may wish to obtain spare embryos which will be cryopreserved for future use in case of failure or of desire for a second child without the woman undergoing a new ovarian stimulation with fertility drugs.

The controlled ovarian hyperstimulation protocol should be tailored individually for each couple to achieve best results and avoid complications. For this reason, the treatment of women undergoing ovarian stimulation must be exclusively performed by experienced physicians who are specialized in IVF. Women who follow an ovarian hyperstimulation program may resume all everyday activities while devoting some of their time to a close monitoring whenever this is indicated by the attendant physician. Ovarian stimulation is achieved by applying a specific stimulation protocol which is individually selected for each case. The drugs used in ovarian stimulation protocols are the following:

- Gonadotropins: they stimulate the ovaries; are administered by injection (usually subcutaneous through the abdomen or thigh using a small insulin-type syringe or an easy-to-use pen); must be administered the same time on an everyday basis; their dosage (number of units to be administered) is adapted according to the woman’s features and re-adapted according to the ovarian response. Several gonadotropin preparations exist according to the prevalent hormone (FSH, LH, or their combination) and to their origin (such as recombinant hormones or purified human hormones)

- Hypothalamic Gonadotropin releasing hormone’s (GnRH) analogues: The administration of such substances suppresses the production of endogenous gonadotropins (i.e. those produced by the woman’s pituitary gland). This suppression is essential for our stimulation protocols as it allows us to gain full control of the situation (once we are able to regulate ovarian stimulation by exogenous gonadotropin injections) and it also ensures us that no acute increase in endogenous LH production will occur as the latter would unavoidably result in untimely ovulation leading to failure of the whole attempt. There are two basic analogue types (agonists and antagonists) that differ in the time span needed to achieve pituitary suppression. The analogues are administered the same time on a daily basis by form of subcutaneous injection or more rarely via nose inhalation.

- Chorionic gonadotropin (human or recombinant): it is administered by a single dose injection at the appropriate time (depending on the follicles’ growth and the scheduled time for egg collection); it induces final follicle maturation and ovulation.   

There are several controlled ovarian hyperstimulation protocols that differ in when the analogue-induced suppression begins. According to the long protocol, we begin with a daily analogue injection at the cycle preceding the one of stimulation (about seven days before the expected first day of menstruation); after the beginning of menstruation and after the success of suppression is proven by measurement of blood estradiol levels we begin stimulating the ovaries through gonadotropin administration. According to the short protocol, we begin the administration of analogue injections at the 2^nd day of menstruation, and at the 3^rd day we begin the administration of gonadotropin injections. Finally, according to the antagonist protocol we start with gonadotropin injections at the 2^nd day of menstruation, adding the antagonist injections when the growing follicles reach an average diameter of 14-15 mm which happens at the 6^th to 7^th day of stimulation.

A close surveillance of the woman undergoing ovarian hyperstimulation is imperative, and must include serial ultrasound scans and blood estrogen measurements. When short protocols are applied, an ultrasonographic and/or hormonal evaluation should be done before starting with the administration of injections, while in the case of long protocols it would be useful if the suppression success was established by hormonal evaluation and then the stimulation injections would follow. At the 5^th-7^th day of stimulation the first ultrasonographic evaluation of the treatment is done, and thereafter this evaluation is repeated every 24-48 hours. Whatever the applied protocol is, when the follicles have gained a satisfactory growth and thus produce adequate estradiol levels the woman will be asked to do the chorionic gonadotropin injection at some time late in the evening (32-36 hours before the scheduled oocyte retrieval). A non-injection day follows, and one day later the oocyte retrieval is scheduled.