Cryopreservation and frozen embryo transfer (FET)
Surplus embryos of day 3 top quality embryos or good-morphology Day 5 or
6 blastocysts in the long agonist
group and all the viable embryos/blastocysts in the PPOS group were
cryopreserved using vitrification. Those who did not get pregnant in the
stimulated IVF cycle and those who
postponed embryo transfer would undergo frozen embryo transfer (FET) at
least 2 months after the stimulated cycle if they had at least one
frozen embryo.
Vitrification was performed with MediCult Vitrifification Cooling
(Origio, Denmark) using ethylene glycol, propylene glycol, sucrose as
cryoprotectant. Embryos were vitrified one by one at room temperature.
For the warming procedure following vitrification, the straw was cut and
the capillary was pulled from the straw out of the liquid nitrogen, and
immediately warmed one by one using MediCult Vitrification Warming
(Origio, Denmark). After warming, embryos were transferred to a culture
dish for evaluation and further embryo development. Only embryos with
more than 50% of blastomeres present after thawing were transferred in
FET cycles.
FETs were carried out in natural cycles for ovulatory women and in
clomiphene induced or hormonal cycles for anovulatory women. Up to two
embryos or blastocysts were transferred in FET cycles.