Embryo transfer
In the past, embryos created through in vitro fertilisation (IVF) were usually transferred to the uterus on day 2 or 3 after egg retrieval. Today, embryos can be cultured outside the uterus for 5 or 6 days until they reach the blastocyst stage.
Advantages Compared with Early Embryo Transfer:
1. Optimising the Chance of Pregnancy
2. Reducing the Risk of Multiple Pregnancy:
By allowing an embryo to develop in the laboratory to day 5 or 6, we can assess its quality more accurately and give couples better-informed advice about which embryos are suitable for cryopreservation and how many embryos should be transferred.
Under Greek law, women under the age of 40 may not have more than two embryos transferred, while women over 40 may not have more than four transferred.
Younger women with high-quality blastocysts suitable for transfer may have a single embryo transferred without reducing their chance of pregnancy. This minimises the risk of a multiple pregnancy, while any remaining suitable embryos can be cryopreserved.
3. Timing That Reflects Natural Development
In natural conception, fertilisation occurs in the fallopian tube. The developing embryo continues to divide and normally reaches the uterus at the blastocyst stage, around day 5 after fertilisation. A day-5 transfer therefore reflects this natural developmental timing.
4. Confirming Embryo Quality Before Cryopreservation:
For couples with a good prognosis, surplus embryos may be cryopreserved at the blastocyst stage. Embryos that do not reach the blastocyst stage by day 5 or 6 are less likely to result in a successful pregnancy. We therefore recommend cryopreserving good-quality blastocysts, which have a high chance of surviving the freeze–thaw process (over 90%).
Ioannis A. Sklavounos MD MSc DFFP
Consultant Obstetrician and Gynaecologist
Specialist Training and Fellowship in the United Kingdom
T.Senior Clinical Fellow – Liverpool Woman’s Hospital UK
IVF
