When the Lister Fertility Clinic 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.
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.
The table below and related chart to the right show how livebirth rate at every age-group is improved when blastocysts are available for transfer.
|Age group||All couples||Blastocyst 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%).