Embryo cryopreservation: proposal for a new indicator of efficiency

Fresh embryo transfer versus frozen embryo transfer in in vitro fertilization cycles: a systematic review and meta-analysis

OBJECTIVE

To examine the available evidence to assess if cryopreservation of all embryos and subsequent frozen embryo transfer (FET) results in better outcomes compared with fresh transfer.

DESIGN

Systematic review and meta-analysis.

SETTING

Centers for reproductive care.

PATIENT(S)

Infertility patient(s).

INTERVENTION(S)

An exhaustive electronic literature search in MEDLINE, EMBASE, and the Cochrane Library was performed through December 2011. We included randomized clinical trials comparing outcomes of IVF cycles between fresh and frozen embryo transfers.

MAIN OUTCOME MEASURE(S)

The outcomes of interest were ongoing pregnancy rate, clinical pregnancy rate, and miscarriage.

RESULT(S)

We included three trials accounting for 633 cycles in women aged 27-33 years. Data analysis showed that FET resulted in significantly higher ongoing pregnancy rates and clinical pregnancy rates.

CONCLUSION(S)

Our results suggest that there is evidence that IVF outcomes may be improved by performing FET compared with fresh embryo transfer. This could be explained by a better embryo-endometrium synchrony achieved with endometrium preparation cycles.

Hollow fiber vitrification: a novel method for vitrifying multiple embryos in a single device

Current embryo vitrification methods with proven efficacy are based on the minimum volume cooling (MVC) concept by which embryos are vitrified and rewarmed ultrarapidly in a very small amount of cryopreserving solution to ensure the high viability of the embryos. However, these methods are not suitable for simultaneously vitrifying a large number of embryos. Here, we describe a novel vitrification method based on use of a hollow fiber device, which can easily hold as many as 40 mouse or 20 porcine embryos in less than 0.1 μl of solution. Survival rates of up to 100% were obtained for mouse embryos vitrified in the presence of 15% DMSO, 15% ethylene glycol and 0.5 M sucrose using the hollow fiber vitrification (HFV) method, regardless of the developmental stage of the embryos (1-cell, 2-cell, morula or blastocyst; n = 50/group). The HFV method was also proven to be effective for vitrifying porcine in vitro- and in vivo-derived embryos that are known to be highly cryosensitive. For porcine embryos, the blastocyst formation rate of in vitro maturation (IVM)-derived parthenogenetic morulae after vitrification (48/65, 73.8%) did not decrease significantly compared with non-vitrified embryos (59/65, 90.8%). Transfer of 72 in vivo-derived embryos vitrified at the morula/early blastocyst stages to 3 recipients gave rise to 29 (40.3%) piglets. These data demonstrate that the HFV method enables simultaneous vitrification of multiple embryos while still adhering to the MVC concept, and this new method is very effective for cryopreserving embryos of mice and pigs.