Fertilization, embryo development, and clinical outcome of immature oocytes obtained from natural cycle in vitro fertilization

To analyze the fertilization, embryo development, and clinical outcome of immature oocytes obtained from natural cycle IVF in women with regular cycles. Natural cycle IVF was performed in 28 patients who had normal ovaries, > 6 antral follicle counts and were less than 40 years old (n = 28 cycles). An hCG trigger of 10,000 IU was administered 36 h before oocyte collection when the diameter of the dominant follicle (DF) was over 12 mm. Oocytes were retrieved from DF as well as from the cohort of smaller follicles. Embryological aspects of the mature and immature oocytes retrieved from these cycles as well as the implantation and clinical pregnancy rates depending on the origin of the embryos transferred were evaluated. Overall clinical pregnancy and implantation rates were 20.8 % and 6.7 %, respectively. There were no differences in in vitro maturation (IVM), fertilization and embryo development between immature oocytes retrieved with and without in vivo matured oocytes. However, the clinical and implantation rates in cycles with embryos produced from in vivo matured oocytes transferred were better than the cycles where only IVM embryos were transferred (30.8 %, 9.1 % vs. 9.1 %, 3.2 %). Although our results show that immature oocytes from natural cycle IVF can fertilize normally and can be used to increase the number of embryos available for transfer, the embryos derived from the immature oocytes in natural cycles IVF have a poorer reproductive potential.