**5.2 Ovarian response to stimulation**

The goal of ovarian stimulation is the collection of multiple dominant follicles in an effort to compensate for the inefficiencies of embryology culture, embryo selection, thus improving chances for successful conception in IVF [129]. The definition of poor ovarian response (POR) should be understood as an essential inability of woman's ovaries to properly react to the selected stimulation [130]. At least two of the following three features must be present for the POR to be diagnosed: 1) advanced maternal age (≥40 years), or any other risk factor for POR; 2) a previous POR (≤3 oocytes with a conventional stimulation protocol); 3) an abnormal ovarian reserve test (antral follicle count: 5–7 follicles, or Anti-Mullerian hormone 0.5–1.1 ng/ml) [131–133].

There are many risk factors that may cause poor ovarian response: short menstrual cycle, single ovary, ovarian cystectomy, smoking, unexplained infertility, previous chemotherapy and/or radiotherapy treatment, family history of premature menopause, pelvic infection, etc. Further studies are needed to elucidate the role of these factors in RIF.
