PCR sexing and developmental rate differences in preimplantation mouse embryos fertilized and cultured in vitro

A two-step polymerase chain reaction (PCR) assay was used to determine the sex of mouse preimplantation embryos obtained from oocytes fertilized and cultured in vitro, to investigate the differences in the developmental rates of mouse embryos according to the sex. All the in vitro developed embryos could be analyzed by this method. When the embryos were classified according to the time of morula to blastocyst transition as fast-intermediate- and slow-growing embryos, a significantly high percentage (78.0%) of the fast-developing embryos were identified as males; while a significantly lower percentage (42.5%) of slow-developing embryos were identified as males. The intermediate-developing embryos presented a sex ratio not significantly different from the total (57.5%). The deviation of sex ratio was further confirmed by embryo transfer experiment, where fast- and slow-developing embryos gave 76.2% and 25.7% male fetuses, respectively. We concluded that male mouse embryos fertilized and cultured in vitro develop faster than female embryos.