Prospective randomized comparison of human oocyte cryopreservation with slow-rate freezing or vitrification.
OBJECTIVE
To compare cryopreservation of mature human oocytes with slow-rate freezing and vitrification and determine which is most efficient at establishing a pregnancy.


METHODS
Prospective randomized.


METHODS
Academically affiliated, private fertility center.


METHODS
Consenting patients with concerns about embryo cryopreservation and more than nine mature oocytes at retrieval were randomized to slow-rate freezing or vitrification of supernumerary (more than nine) oocytes.


METHODS
Oocytes were frozen or vitrified, and upon request oocytes were thawed or warmed, respectively.


METHODS
Oocyte survival, fertilization, embryo development, and clinical pregnancy.


RESULTS
Patient use has resulted in 30 thaws and 48 warmings. Women's age at time of cryopreservation was similar. Oocyte survival was significantly higher following vitrification/warming (81%) compared with freezing/thawing (67%). Fertilization was more successful in oocytes vitrified/warmed compared with frozen/thawed. Fertilized oocytes from vitrification/warming had significantly better cleavage rates (84%) compared with freezing/thawing (71%) and resulted in embryos with significantly better morphology. Although similar numbers of embryos were transferred, embryos resulting from vitrified oocytes had significantly enhanced clinical (38%) pregnancy rates compared with embryos resulting from frozen oocyte (13%). Miscarriage and/or spontaneous abortion rates were similar.


CONCLUSIONS
Our results suggest that vitrification/warming is currently the most efficient means of oocyte cryopreservation in relation to subsequent success in establishing pregnancy.
Smith
Gary D
GD
Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan, USA.
Serafini
Paulo C
PC
Fioravanti
Joyce
J
Yadid
Isaac
I
Coslovsky
Marcio
M
Hassun
Pericles
P
Alegretti
José Roberto
JR
Motta
Eduardo L
EL
D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D004624:Embryo Transfer / Q000379:methods; D005260:Female; D005306:Fertilization / Q000502:physiology; D005615:Freezing; D006801:Humans; D009865:Oocytes; D010062:Ovulation Induction / Q000379:methods; D011247:Pregnancy; D018873:Pregnancy Rate; D020554:Sperm Injections, Intracytoplasmic / Q000379:methods; D013997:Time Factors