Cryopreservation and frozen-thawed embryo transfer (FET)
All the day 3 top quality embryos and good-morphology Day 5 or 6
blastocysts were cryopreserved using a vitrification protocol. Women in
both groups would undergo frozen–thawed embryo transfer (FET) at least
2 months after the stimulated cycle if they had at least one frozen
embryo. FETs were carried out in natural cycles for ovulatory women and
in clomiphene induced or hormone replacement cycles for anovulatory
women. 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. Up to two embryos or blastocysts were transferred in each
FET cycle.
Luteal
phase support was given by vaginal or intramuscular progesterone at the
discretion of the attending physicians. A urine pregnancy test was
carried out 2 weeks after the transfer. Those with a positive urine
pregnancy test were scanned after 2 weeks to identify the number and
presence of a gestation sac with a fetal pole. All pregnant women were
contacted or traced for the pregnancy outcomes after delivery or
miscarriage.