A. Baker et al., PREGNANCY ACHIEVED WITH PRONUCLEAR-STAGE EMBRYOS THAT WERE CRYOPRESERVED AND THAWED TWICE - A CASE-REPORT, Journal of assisted reproduction and genetics, 13(9), 1996, pp. 713-715
Purpose: Our purpose was to determine if pronuclear-stage embryos (2PN
) could be thawed, then frozen again with subsequent survival and clea
vage after thawing. Methods: A simplified cryopreservation protocol wa
s used in which a slow cooling program is started at the seeding tempe
rature of -6 degrees C in an alcohol-bath controlled-rate freezer 1,2-
Propanediol (1.5 M) was added to embryos before cooling. A fast thawin
g technique at room temperature was used. The cryoprotectant was remov
ed in one step using a 1 M sucrose solution. Results: Three months aft
er refreezing, the three 2PN embryos were thawed and all three cleaved
after 24 hr in culture. Following embryo transfer a pregnancy was ach
ieved and a healthy full-term baby girl was born. Conclusions: This is
the third case reported of successful pregnancies after transfer of h
uman embryos that were frozen twice before transfer and the first case
where the second freeze occurred at the pronuclear stage. This is als
o the first successful refreezing of human embryos using a simplified
freezing and thawing technique with one-step addition and removal of c
ryoprotectant.