Embryo transfer is a critical step in the IVF process where the fertilized embryos are placed into the woman’s uterus to achieve pregnancy. There are several types of embryo transfers that differ based on timing, embryo development stage, and the number of embryos transferred.
Here’s a detailed look at the most common types:
Fresh Transfer
A fresh embryo transfer occurs in the same cycle as the egg retrieval and fertilization. After eggs are collected and fertilized in the lab, the best quality embryo(s) are transferred into the uterus usually 3 to 5 days later. This transfer is performed without freezing the embryos and capitalizes on the immediate readiness of the uterus after ovarian stimulation.
Frozen Transfer
Frozen embryo transfer (FET) involves thawing embryos that were frozen from a previous IVF cycle before placing them into the uterus. This approach allows flexibility in timing and often results in better synchronization of the endometrium for implantation. FETs are increasingly preferred due to improved success rates, especially when preimplantation genetic testing is performed.
Cleavage (Day 3) Transfer
In cleavage-stage transfers, embryos are transferred on the third day after fertilization when they typically have 6 to 8 cells. These earlier-stage transfers are common but may have slightly lower implantation potential compared with blastocyst transfers because the embryo has had less time for natural selection.
Blastocyst (Day 5) Transfer
Blastocyst transfer happens on the fifth day post-fertilization when the embryo has developed into a more advanced stage, usually containing 100 cells and ready for implantation. Blastocyst transfers tend to have higher success rates as the embryo’s viability is better assessed, and uterine receptivity is optimal at this time.
Single Embryo Transfer
Single embryo transfer (SET) involves transferring only one embryo to minimize the risks associated with multiple pregnancies such as preterm birth. It is recommended especially for younger women or when high-quality embryos are available. SET balances maximizing pregnancy chances while reducing health risks to mother and child.
Multiple Embryo Transfer
Multiple embryo transfers are performed when more than one embryo is placed to increase the chances of pregnancy, particularly in cases with lower embryo quality or advanced maternal age. However, this increases the risk of multiple pregnancies, which require careful consideration and counseling.
Conclusion
Choosing the right type of embryo transfer depends on various factors including embryo quality, maternal age, and fertility clinic recommendations. Fresh and frozen transfers each have advantages, while the choice between cleavage-stage and blastocyst transfer affects implantation success. Considering single versus multiple embryo transfer is crucial for balancing success rates with pregnancy safety. A personalized approach helps optimize outcomes in the exciting journey of assisted reproduction.