LAUSR

Abstract Aim We compared the clinical outcomes of vitrified–thawed cycles during in vitro fertilization (IVF) for frozen and thawed blastocysts compared to cleavage-stage embryos that were frozen, thawed and extended culture to the blastocyst stage. Material and methods Between January 2014 and December 2016, 908 frozen-thawed cycles were included in the study. After removing cycles that met exclusion criteria, clinical outcomes for 355 cleavage-stage embryos with extended blastocyst culture (Group I) were compared with 279 frozen and thawed blastocysts (Group II). Results Cryo-survival rate of the two groups were similar (96.7% versus 95.0%). Implantation rates (28.9% versus 22.4%, p = .04) and clinical pregnancy rates (37.2% versus 27.9%, p = .03) were higher in Group I. Pregnancy, live birth and abortus rates were similar in both groups. Although overall abortus rates were similar in both groups, abortus rates before 12 weeks of gestation were higher in Group I, and chemical abortus rates were higher in Group II (p = .03, p = .04). Weeks of gestation at birth and birth weight were similar in both groups. Conclusions The use of extended blastocyst culture of cleavage-stage embryos was not inferior to frozen and thawed blastocysts. Freezing at the cleavage-stage can provide similar cryo-survival rates than blastocyst vitrification. Vitrifying surplus or all embryos for storage at the cleavage-stage allows higher implantation and clinical pregnancy rates. But after abortus, live birth rates were similar in both groups.