Mouse embryos generated from frozen-thawed oocytes can successfully survive a second cryopreservation.
BACKGROUND
To determine whether mouse embryos generated from frozen-thawed oocytes can successfully survive a second cryopreservation.


METHODS
Immature C57BL6*BALB/c female mice underwent superovulation and the collected oocytes were divided into three groups. Group A oocytes (n = 107) underwent IVF. Group B oocytes (n = 167) underwent IVF and embryos generated were then cryopreserved. Group C oocytes (n = 94) were cryopreserved, thawed and underwent IVF. Two-four-cell stage embryos were re-cryopreserved and thawed. Embryos from all groups were then cultured to the blastocyst stage.


RESULTS
Cleavage rates to the 2-4-cell stage were 78, 71 and 46% for groups A, B and C respectively. Blastulation rates from 2-4 cell-stage embryos were 37/83 (45%), 27/118 (23%) and 8/35 (23%) for groups A, B and C respectively. Development to blastocysts was observed in 37/107 oocytes (35%), 27/167 oocytes (16%) and only 8/94 oocytes (9%) for groups A, B and C respectively.


CONCLUSIONS
Oocyte cryopreservation results in reduced fertilization rates. Embryo cryopreservation reduces blastulation rates by half regardless of whether the oocytes were fertilized fresh or frozen-thawed. Nevertheless, embryos generated from cryopreserved oocytes can survive cryopreservation and develop to the blastocyst stage at rates comparable with embryos obtained from fresh oocytes.
Revel
Ariel
A
In Vitro Fertilization Unit, Department of Obstetrics and Gynecology, Hadassah University Hospital, Ein Kerem, Jerusalem, Israel. Revel@md.huji.ac.il
Moshe
Naama
N
Helman
Aharon
A
Safran
Anat
A
Simon
Alex
A
Koler
Moriah
M
D000818:Animals; D001755:Blastocyst / Q000502:physiology; D002970:Cleavage Stage, Ovum; D015925:Cryopreservation; D046508:Culture Techniques; D004622:Embryo, Mammalian / Q000502:physiology*; D005314:Embryonic and Fetal Development; D005260:Female; D005306:Fertilization; D005307:Fertilization in Vitro; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009865:Oocytes / Q000502:physiology