Hu KL, Zhang D, Li R, et al. - Via performing this retrospective cohort study of 21,648 women who underwent frozen single-blastocyst transfer, researchers here examined if endometrium preparation associates with perinatal outcomes. Observations revealed association of hormone replacement cycles with an elevated risk of preterm delivery, very preterm delivery, cesarean delivery, low birth weight, macrosomia, premature rupture of membrane, and hypertensive disorders of pregnancy, compared with natural cycles. An increased risk of postterm delivery and gestational diabetes mellitus was observed in correlation with stimulated cycles. No statistically significant difference was noted in the rate of SGA, placenta previa, or congenital abnormality among the three endometrium preparation methods.