During the study period only single embryo transfers were performed in our center and an exclusive SET policy was strictly observed. Patients were counseled accordingly before their treatment started about the risk of multiple pregnancies, the benefits of an elective single embryo transfer and the possibility of embryo cryopreservation. Approximately, half of the embryo transfers (47.1 %) were performed at day 2 or 3 with a fresh cleavage-stage embryo whereas in most of the remaining cases (47.4 %) embryos were cultured to blastocyst-stage and vitrified electively for subsequent use in frozen-thawed blastocyst transfer cycles. Details of the vitrification method using the Cryotop® (Kitazato, Japan) were described previously [5 (link)]. Elective frozen-thawed blastocyst transfer was preferred in the presence of tubal factor infertility (tubal obstruction, hydrosalpinx or the history of extrauterine pregnancy) or recurrent implantation failures with cleavage-stage embryos.
Frozen-thawed embryo transfers were performed in spontaneous natural or hormonal replacement cycles. In natural cycles, cleavage-stage embryos and blastocysts were transferred on day 2 and 5 respectively after ovulation was confirmed. In hormonal replacement cycles, transdermal estradiol patches were started from cycle day 2 and dydrogesterone was added from cycle day 11 after which cleavage-stage embryos or blastocysts were transferred 1 or 7 days later, respectively. All embryo transfer procedures were performed under vaginal ultrasound guidance using a specially designed soft catheter (Kitazato, Japan) by placing a single embryo in minimal volume to the mid-uterine cavity [6 (link)]. Dydrogesterone (30 mg/day orally) was routinely administered during the early luteal phase both after fresh and frozen-thawed embryo transfer procedures. Moreover intramuscular or intravaginal progesterone was also added until the 9th pregnancy week in cases where the endogenous progesterone production from the placenta was found to be insufficient.
Frozen-thawed embryo transfers were performed in spontaneous natural or hormonal replacement cycles. In natural cycles, cleavage-stage embryos and blastocysts were transferred on day 2 and 5 respectively after ovulation was confirmed. In hormonal replacement cycles, transdermal estradiol patches were started from cycle day 2 and dydrogesterone was added from cycle day 11 after which cleavage-stage embryos or blastocysts were transferred 1 or 7 days later, respectively. All embryo transfer procedures were performed under vaginal ultrasound guidance using a specially designed soft catheter (Kitazato, Japan) by placing a single embryo in minimal volume to the mid-uterine cavity [6 (link)]. Dydrogesterone (30 mg/day orally) was routinely administered during the early luteal phase both after fresh and frozen-thawed embryo transfer procedures. Moreover intramuscular or intravaginal progesterone was also added until the 9th pregnancy week in cases where the endogenous progesterone production from the placenta was found to be insufficient.
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