【Abstract】 Objective　To observe the effect of in vitro fertilization (IVF) following superovulation on thedevelopment of mouse blastocysts. Method Based on the key procedures of IVF, including

superovulation,IVF, in vitro embryo culture, five groups were set up: natural mating group (n=8), superovulation + naturalmating group (n=8), in vitro culture group (n=5), superovulation + in vitro culture group (n=6), IVF group(n=15). According to Gardner's classification standard, the development status of mouse blastocysts wasobserved at E3.5. The ratio of hatched area of stage Ⅴ blastocysts was compared between superovulation + invitro culture group and IVF group, and the survival rate of fetuses after transferring of IVF mouse blastocystswas analyzed. The statistical methods were performed by Chi-square test and Mann-Whitney nonparametrictest. Result The constitute ratios of different blastocyst stages ( Ⅰ - Ⅴ ) in IVF group significantly differedfrom other four groups (the global χ2=188.200, P<0.001). At E3.5, blastocysts in IVF group were mainlyat the stage Ⅲ - Ⅴ , accounting for 74.5%, and the ratio of stage Ⅴ blastocysts reached to 51.2%, andblastocysts in other four groups were mainly at the stage Ⅲ and Ⅳ . The ratio of the hatched area of stage Ⅴblastocysts in IVF group was significantly higher than that in superovulation + in vitro culture group [0.11（0.05，0.18） vs 0.04 （0.02，0.07）, P<0.017], and the hatched area ratio of stage Ⅴ blastocysts in IVF groupshowed skewed distribution. After blastocysts transferring, the survival rate of fetuses at E12.5 in IVF groupwas significantly lower compared to in vitro culture group (45.3% vs 63.4%, χ2=8.647, P<0.05). Moreover,when transferring IVF blastocysts with different hatched area ratio (<5% vs 5%-10%) to uteruses, the datashowed that the survival rate of fetuses at E12.5 from blastocysts (<5% hatched area) was robustly higherthan blastocysts (5%-10% hatched area) (52.5% vs 29.7%, χ²=7.578, P<0.05). Conclusion IVF followingsuperovulation leads to asynchronous development of mouse blastocysts, and IVF blastocysts with largehatched area (5%-10%) have lower survival rate after transferring.