Fertilization and Development of Conjoined Human Oocyte from a Binovular Follicle Containing Two Individual Oocytes Surrounded by a Zona Pellucida

Abstract The most reliable definition of conjoined oocytes is the inclusion of two oocytes within a common zona pellucida(ZP) or their fusion in the zonal region. Because the available data are extremely limited, the significance of conjoined oocytes in IVF laboratory setting has been questionable. We analyzed the characteristics of 18 patients with conjoined oocytes in our center. The maturation of conjoined oocytes were asynchronous. Most of the cases were that one oocyte in each pair of conjoined oocytes was in the MII stage and the other was in the GV stage. The maturation rate and fertilization rate of conjoined oocytes were significantly lower than that of normal oocytes. There was no significant difference in the rate of cleavage and D3 High-quality embryo, but the rate of blastocyst formation of conjoined oocytes decreased significantly. The area of larger oocytes in conjoined oocytes was not different from that of normal oocytes, and its companion was significantly smaller than that of normal oocytes. The mean ZP thickness of all oocytes, larger or smaller, was significantly thinner than that of normal oocytes. After analyzing the clinical characteristics of the patients, it was suggested that the higher estrogen level or the more number of maturation follicles on HCG day were more likely to promote the emergence of conjoined oocytes.