Main Findings
In this retrospective study, the results indicated that female age, quality and number of transferred blastocysts had significant effects on pregnancy outcomes. IR, CPR and LBR of the same blastocyst transfer groups were observed to decrease gradually with age. Moreover, increasing the transferred number of same grade blastocysts did not obviously increase CPR and LBR, but, it significantly increased MPR. For double blastocyst transfer, the better-quality the transferred blastocysts were, the higher the IR, CPR, MPR and LBR were. In addition, the singleton group had a higher average gestational age and birthweight as well as a lower cesarean section rate, preterm labor rate and low birthweight rate than the twin group. Monozygotic twins had a lower gestational age and birthweight in conjunction with a higher preterm birth rate and low birthweight rate than dizygotic twins. There was a positive correlation between sex ratio (male/female) and the proportion of good-quality blastocysts, and the difference was found to be significant between good-quality and poor-quality blastocyst groups.