Introduction

Ovarian response can be defined as the endocrine and follicular reaction of the ovaries to a stimulus. The term is used in clinical research and practice both qualitatively (for example, achieving growth of a single dominant follicle and ovulation in anovulatory women undergoing ovulation induction) and quantitatively (for example, the extent of multifollicular development in ovulating women undergoing ovarian stimulation for in vitro fertilisation). Achieving a distinct ovarian response usually represents the desired outcome of pharmacological interventions on the hypothalamic–pituitary–ovarian axis in ovulation induction and ovarian stimulation. The considerable individual variability in ovarian response to stimulation, however, necessitates close monitoring and dose adjustment for each woman. The likelihood of pregnancy in a woman undergoing ovulation induction is subject to a large number of factors other than ovarian reserve and ovarian response.

It is of high clinical relevance to identify predictors of ovarian response that will enable clinicians to individualise ovulation induction strategies, thereby minimising complications and the risk of treatment failure while maximising the chances of a continuing pregnancy. The conventional paradigm in many areas of reproductive medicine has been ‘one size fits all’ or a choice of therapy based on the physician's experience from their own clinical practice, which may have low reproducibility. To improve consistency between clinics, various clinical, endocrine and ovarian ultrasonographic and genetic characteristics have been explored for use as predictors of ovarian response.