A unique biological in-vivo model to evaluate follicular development during in-vitro maturation treatment

The aim of this study was to identify the size in which the dominant follicle acquires the ability to produce a functional corpus luteum. This observational study includes 15 women with ovulatory cycles who underwent human chorionic gonadotrophin (HCG)-primed in-vitro maturation (IVM) treatments without embryo transfer. All patients received subcutaneous injection of HCG 10,000 IU 38 h prior to oocyte retrieval. Five to seven days following retrieval, serum concentrations of progesterone and oestradiol were measured along with ultrasound scan measuring the antral follicle count. Using receiver operating characteristic curves and the Youden index (J), this study clearly shows that the diameter of the dominant follicle at the time of the LH surge is a good predictor for its ability to form a progesterone-producing corpus luteum (area under the curve 0.94). These findings revealed that the dominant follicle develops the competence to form a corpus luteum, signified by the production of more than 10 nmol/l serum progesterone at 5–7 days from oocyte retrieval, as soon as it acquires a diameter of 10.5–12.0 mm. In addition, a new cohort of viable antral follicles can be identified as early as 5–7 days following IVM oocyte retrieval.During the normal monthly cycle in women, usually one dominant follicle grows and ovulates in response to the LH surge. Following ovulation the ovulated follicle transforms into a corpus luteum which secrets the hormone progesterone. Progesterone affects the uterine endometrium to support the process of implantation of the fertilized oocyte, a process that is crucial for a normal pregnancy to occur. We discovered that only when the dominant follicle reaches the size of between 10.5 and 12 mm, it obtains its ability to respond to the LH surge and become a progesterone-secreting corpus luteum able to support pregnancy.