Fresh embryos versus freeze-all embryos - transfer strategies: Nuances of a meta-analysis

Abstract

ObjectiveThe present meta-analysis aimed to evaluate whether the freeze-all strategy (Freeze/All-ET) could bring about improvements in the clinical assisted reproductive technique (ART) outcomes when compared with the fresh embryo transfer strategy (Fresh-ET) in patients undergoing an ART cycle in accordance with the mean number of oocytes collected.MethodsA systematic review based on electronic searches in databases (PubMed, EMBASE, Web of Science, SCOPUS, and Cochrane Central Register of Controlled Trials) was carried out to identify randomized controlled trails (RCTs) comparing ART outcomes between fresh-embryo transfers versus elective frozen-embryo transfers up to February of 2017. Four reviewers independently evaluated abstracts, validity assessment and data extraction. Odds Ratio (OR) values with a 95% confidence interval (CI), and heterogeneity were evaluated.ResultsFive RCTs were included as targets for data extraction and meta-analysis purposes. The results of this meta-analysis were divided into two parts (Freeze/All-ET versus Fresh-ET): Part I- All trials in which the mean number of collected oocytes was >12 and <21 for ongoing pregnancy rate (OR=1.24; 95%CI=1.06-1.44), clinical pregnancy rate (OR=1.19; 95%CI=0.98-1.43), live birth rate (OR= 1.39; 95%CI=0.99-1.95), and miscarriage rate (OR=0.68; 95%CI=0.46-1.00); Part II- Three studies where the mean number of oocytes retrieved was >12 and <15 for ongoing pregnancy rate (OR=1.17; 95%CI=1.00-1.38), clinical pregnancy rate (OR=1.34; 95%CI=0.79-2.28), live birth rate (OR= 1.24; 95%CI=1.00-1.55), and miscarriage rate (RR=0.68; 95%CI=0.46-1.02).ConclusionsThe freeze-all strategy could be favorable when high numbers of oocytes are collected, signaling an association between higher ovarian stimulation and consequent impairment of endometrial receptivity. However, when the mean number of oocytes collected is <15, the freeze-all strategy does not appear to be advantageous.

Chromosomal analysis in IVF: just how useful is it?

“…Independent of PGD, the IVF world generally has seen improvement in embryo cryopreservation techniques which later impacted the world of PGT-A. Indeed, in recent years, there has been a move in the direction of embryo cryopreservation with a view to a later transfer (freeze-all) strategy in an unstimulated cycle (Dieamant et al 2017). Thus, while increased pregnancy success rates have been attributed to the advancement of PGT-A technologies (improved blastocyst biopsy (previous section) and aCGH, NGSsee next sections), some argue that credit may possibly be given to an improvement associated with frozen embryo transfer (Dieamant et al 2017).…”

“…Indeed, in recent years, there has been a move in the direction of embryo cryopreservation with a view to a later transfer (freeze-all) strategy in an unstimulated cycle (Dieamant et al 2017). Thus, while increased pregnancy success rates have been attributed to the advancement of PGT-A technologies (improved blastocyst biopsy (previous section) and aCGH, NGSsee next sections), some argue that credit may possibly be given to an improvement associated with frozen embryo transfer (Dieamant et al 2017). Transfer of vitrifiedwarmed single blastocysts yields improved outcomes (Roy et al 2014) and higher live birth rates (77% vs 59%) in the frozen group compared with the fresh group (Coates et al 2017), which could be attributed to a better preparation of endometrium in the next cycle avoiding the possible detrimental effect of ovarian hyperstimulation on endometrial receptivity.…”

“…There is a tight connection between the window of implantation and the endometrial transcriptome (Mahajan et al 2015, Koot et al 2016 where natural cycles have been shown to be superior over artificial cycles based on specific gene expression profiles (Altmäe et al 2016). Therefore, transfer in subsequent freeze-thaw cycles may also allow for preparation of a more physiological and receptive endometrium (Dieamant et al 2017).…”

Laser collapse performance in blastocysts applied before vitrification

“…14 Therefore, many studies have been reported showing reduced time of the cryopreservation procedure, aiming to eliminate the high costs with equipment and also to improve the quality of frozen and thawed embryos in order to promote good results in the pregnancy rate. 8,11,15 One way to achieve these goals was through the use of vitrification techniques, which, other than slow freezing, requires a radical increase in both the concentration of the cryoprotectants and the rate of cooling. 16,17 Current procedures describe that the exposure of the suspended cells in a small volume of cryoprotectants in high concentration, for a short period of time and placed at low temperature directly on nitrogen liquid at -196 ° C does not allow the formation of ice crystals.…”

“…[5][6][7] Emphasizing the importance of the TEC, there are many reports that a stimulation in the treatment of IVF and the exposure of women submitted to high hormone levels may alter endometrial receptivity. 8…”