Blastocyst transfer
When we first opened in 1988, embryos were routinely transferred back into the womb two to three days after egg collection. We now have the expertise to grow embryos to five to six days after egg collection, when the pre-implantation embryos are called blastocysts.
Blastocyst transfer will not be suitable for all couples. The decision to offer blastocyst transfer will be made on day 3 post egg collection when it is often difficult to accurately predict which embryos are most likely to produce a pregnancy.
For example if the laboratory team are unable to select the best embryos for transfer because there are a large number of rapidly developing, good quality embryos on day 3, they may suggest delaying the embryo transfer to day 5 or day 6.
This offers significant advantages over early transfer:
1: Improved pregnancy outcome
The genetic make-up of embryos becomes more apparent after Day 3 of development so by waiting to Day 5, we are better able to select the most suitable embryos for transfer.
2: Minimises multiple pregnancy rate
By waiting to Day 5 we can assess embryo quality more accurately and better advise couples of the suitability of embryos for freezing and how many embryos may be best to transfer. Patients under the age of 40 can legally have no more than 2 embryos transferred and patients 40 or over no more than 3. Younger women with high quality blastocyst embryos available for transfer are advised to transfer only 1 embryo as this does not compromise pregnancy outcome, minimises multiple pregnancy rate and any extra embryos can be frozen.
3: Physiological timing of transfer
During natural conception, eggs and sperm fertilise in the fallopian tube, in which they continue to divide and only reach the uterus on Day 5 post fertilization at this blastocyst stage. Therefore a Day 5 transfer mirrors this physiological timing.
4: Confirms embryo quality before freezing
We would only recommend freezing of supernumerary embryos at this stage as if embryos do not reach blastocyst stage by Day 5-6 they will not have the potential to achieve a pregnancy. Similarly, we would only recommend freezing top quality blastocysts to ensure a high chance of surviving the freeze/thaw process (>90%).
Time-lapse imaging (EmbryoScope)
EmbryoScope is the world’s most used time-lapse system that allows embryologists to monitor your developing embryos throughout their development.
At the heart of the system is the EmbryoScope incubator which ensures stable incubation while automatically taking images of the developing embryos at defined intervals over the 2-5 days of development. This information is then transferred to computer software for analysis, which can aid embryo selection by providing a rank of embryo development potential.
Assisted Hatching
Whether embryos are transferred on Day 3 or 5, for implantation and therefore pregnancy to occur, the embryos have to ‘hatch’ out of the zona pellucida (embryo shell) so that the cells of the embryos can come into direct contact with the cells lining the womb. Some studies have suggested that a possible reason for the failure of embryos to implant following IVF treatment may be the inability of embryos to undergo this hatching process.
It is possible to assist this hatching process in the laboratory by using a laser to make a small hole in the shell of the embryo. This process is known as assisted hatching.
There is no evidence of benefit in the routine use of assisted hatching in every cycle and in view of the theoretical risk (<1%) of damage during the procedure it may only be suggested in select cases:
- couples whose embryos are noted to have thickening of the zona by or highly experienced embryological team.
- couples with a history of recurrent implantation failure
- couples with an advanced maternal age.