4 5 6 7 8 Furthermore, the freeze-all strategy offers the advantage of allowing the application of a gonadotropin releasing hormone agonist for final oocyte maturation to minimise the risk of early and late ovarian hyperstimulation syndrome. 1 2 3 Supraphysiological levels of oestradiol and progesterone after ovarian stimulation have been hypothesised to accelerate endometrial advancement and impair endometrial receptivity, reducing the implantation rate in the fresh transfer cycles. Additionally, the practice of elective freezing of all embryos (freeze-all) is becoming more frequent because pregnancy rates after frozen transfers are approaching those of fresh transfer cycles. In recent years, the use of frozen embryo transfers has gradually increased owing to improvements in laboratory techniques such as vitrification and blastocyst culture. Time to pregnancy was longer in the freeze-all group. The risks of pregnancy related, obstetric, and neonatal complications did not differ between the two groups except for a higher mean birth weight after frozen blastocyst transfer and an increased risk of prematurity after fresh blastocyst transfer. No significant differences between groups were observed for positive human chorionic gonadotropin rate or pregnancy loss, and none of the women had severe ovarian hyperstimulation syndrome only one hospital admission related to this condition occurred in the fresh transfer group. Additionally, no significant difference was found in the live birth rate (27.4% (61/223) for the freeze-all group and 28.7% (66/230) for the fresh transfer group risk ratio 0.98, 95% confidence interval 0.87 to 1.10, P=0.83). Results Ongoing pregnancy rate did not differ significantly between the freeze-all and fresh transfer groups (27.8% (62/223) v 29.6% (68/230) risk ratio 0.98, 95% confidence interval 0.87 to 1.10, P=0.76).
Jeanette Bogstad, senior consultant 2,.
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