Blastocyst vitrification, cryostorage and warming does not affect live birth rate, infant birth weight or timing of delivery

Research question: Does vitrification and warming affect live birth rate, infant birth weight and timing of delivery? Design: Retrospective, cohort study comparing outcomes of donor oocyte recipient fresh (n = 25) versus vitrified (n = 86) euploid blastocyst transfers; donor oocyte recipient singleton live births from fresh (n = 100) versus vitrified (n = 102) single embryo transfers (SET); and autologous vitrified euploid SET (n = 1760) (cryostored 21–1671 days). Results: Group 1: fresh and vitrified–warmed blastocysts had similar live birth (OR 1.7; 95% CI 0.5 to 5.9), implantation (OR 0.9; 95% CI 0.2 to 3.9), clinical pregnancy (OR 3.4; 95% CI 0.9 to 13.0) and pregnancy loss (OR 1.2; 95% CI 0.98 to 1.4); group 2: low birth weight (OR 0.44; 95% CI 0.1 to 1.6) and preterm delivery (0.99; 95% CI 0.4 to 2.3) rates were similar in fresh and vitrified–warmed blastocyst transfers; group 3: cryostorage duration did not affect live birth (OR 1.0; 95% CI 1.0 to 1.0), implantation (OR 1.0; 95% CI 0.99 to 1.01), clinical pregnancy (OR 1.0; 95% CI 1.0 to 1.0]), pregnancy loss (OR 0.99; 95% CI 1.0 to 1.0), birth weight (β = −15.7) or gestational age at delivery (β = −0.996). Conclusions: Vitrification and cryostorage (up to 4 years) are safe and effective practices that do not significantly affect clinical outcome after embryo transfer.