Freezing all embryos for later transfer might therefore improve implantation and pregnancy rates and increase the safety of IVF. Presently, the highest success rates in reproductive medicine are seen in the recipients of donor eggs. These are women who have not had ovarian stimulation - their endometrial tissue has not been exposed to high hormone levels, and they are not at risk of OHSS.
However, while the theory of a freeze-all policy seems attractive - and the technique has been commonly employed as a safety measure when OHSS is a threat - no robust systematic studies have indicated whether the cryopreservation of all viable embryos with later frozen embryo transfer (FET) is associated with better outcomes than fresh embryo transfers.
Now, the first meta-analysis on this subject indicates that the chance of a clinical pregnancy is around 30% higher when all embryos are frozen for later transfer than with fresh embryo transfer. The results were presented today at the annual meeting of ESHRE (European Society of Human Reproduction and Embryology) by Professor Miguel Angel Checa from the Hospital Universitari del Mar in Barcelona, Spain.
The study was a systematic review of the entire literature, which provided a pool of 64 relevant studies - with three randomised trials - performed before December 2011. The current review was based on information from 633 IVF/ICSI cycles in which 316 were randomised to fresh embryo transfer and 317 to FET. Results showed - based on a relative risk calculation - that the probability of a clinical pregnancy is significantly higher from freeze-all cycles than in fresh embryo transfers (a relative risk of 1.31, which was statistically significant). The miscarriage rates did not show significantly differences between the two groups.
"The pooled data demonstrates that embryo cryopreservation and subsequent FET may improve the outcome of assisted reproduction treatment," said Professor Checa. The study recorded an ongoing pregnancy rate of 38% in fresh transfer cycles, and 50% in the FET cycles.
Professor Checa also explained why FET in a later non-stimulated cycle might improve IVF results. He noted that the multiple eggs generated by ovarian stimulation will increase release of the hormone estradiol from the ovary, which affects the receptivity of endometrial tissue. In addition, some recent studies have shown that ovarian stimulation causes changes to the endometrial DNA pattern, which are not evident in the normal receptive endometrium.
Professor Checa added that the results of his study were "preliminary", but statistically robust. However, with other groups known to be performing similar studies, he urged patience until their results were known. "We are quite confident with our results," he said. "But in our view we should wait until the end of the year for results from other studies to confirm our data and recommend a change in IVF policy."
He added that, with improvements in the technologies of embryo cryopreservation (through vitrification), the evolution of freeze-thawed embryos in IVF is now comparable to that of fresh embryos. A freeze-all approach may thus extend that success even further - and with a greater degree of safety. "When we freeze all of the embryos, we completely avoid the risk of OHSS," said Professor Checa. "So freezing all the embryos we collect would avoid the biggest complication that exists in assisted reproduction."
From abstract no: O-169 Tuesday 3 July 2012, 15.30 hrs EEST
Fresh embryo transfer versus frozen-thawed embryo transfer in assisted reproduction technique cycles: a systematic review and meta-analysis
Note: When obtaining outside comment, journalists are requested to ensure that their contacts are aware of the embargo on this release.
The 28th Annual Meeting of ESHRE, the world's largest event in reproductive science and medicine, is taking place in Istanbul from 1-4 July 2012
Christine Bauquis | EurekAlert!
Scientists enlist engineered protein to battle the MERS virus
22.05.2017 | University of Toronto
Insight into enzyme's 3-D structure could cut biofuel costs
19.05.2017 | DOE/Los Alamos National Laboratory
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
Dental plaque and the viscous brown slime in drainpipes are two familiar examples of bacterial biofilms. Removing such bacterial depositions from surfaces is...
For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope. Researchers from the University of Basel’s Swiss Nanoscience Institute network have reported the results in the journal Science Advances.
Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds. Molecules and sections of macromolecules are...
22.05.2017 | Event News
17.05.2017 | Event News
16.05.2017 | Event News
22.05.2017 | Materials Sciences
22.05.2017 | Life Sciences
22.05.2017 | Physics and Astronomy