What is Embryo Transfer?

Embryo transfer 

is the process of putting the embryos that are growing in the lab back into the uterus. The period during which the embryos remain in the lab as we have seen in the previous chapter is one where important procedures are undertaken and crucial decisions are made. While growing the embryo is the responsibility of the embryologist, depositing them in the uterus is the job of the clinician.

Embryo transfer can be done during any one of the four stages of embryo development

· Day 2 (cleavage stage)

· Day 3 (cleavage stage)                                                         

· Day 5 (Blastocyst stage)

· Day 6 (Blastocyst stage)

Embryo transfer to be done at which stage of the development?

The first decision which is jointly taken by the embryologist and the clinician is about the stage at which the embryo should be transferred. A number of factors such as the quality of embryos, the number of attempts at IVF the patient has already had among other factors are taken into consideration before taking this decision. 

The preferred time for transfer is usually between Day 2 and Day 6 of the embryo development. The question as to which is the best day for embryo transfer is still under debate. Day 5 transfers may be ideal since in natural conception cycles, embryos typically implant on Day 5 or 6 after ovulation. 

According to this theory, Day-5- or Day-6-blastocyst embryo transfers may be preferable due to the ideal uterine environment conditions at this stage. Embryos transferred at the blastocyst stage often have a higher implantation rate (meaning that they are more likely to “stick” and develop into a healthy pregnancy).

How many embryos need to be transferred?

The next big decision is the number of embryos to be transferred. This decision is taken jointly by the clinician, embryologist and the patient. Keeping in mind, the fact that each embryo is a potential baby, factors such as patient history, age, number of attempts are taken into account. Generally, one or two embryos are selected or transferred to avoid multiple pregnancies. 

Remember, it is just not about conceiving BUT about a heathy pregnancy and taking home a healthy baby. You might ask what if I have eight embryos and I transfer two good embryos to the uterus.  Will the other six embryos go to waste? The answer is no, not at all. The solution to this is vitrification of the good, surplus embryos.

Success of the embryo transfer depends on:

1. Using a strict grading criterion and selecting the best embryos

2. Each transfer done should be the best, there is no point saving the best embryos. If the clinician feels that the endometrium (uterus lining) is not ready, she will freeze the embryos rather than transferring and wasting them.

As is evident, both the embryologist and the clinician play important roles leading to the success of the embryo transfer. The embryologist follows a strict grading criterion and selects the best embryo for transfer and the clinician decides if the endometrium is ready or not. 

A frozen embryo transfer (FET) is a procedure where embryos that were cryogenically-stored (frozen) from a previous IVF or donor egg cycle are thawed and transferred to a uterus as part of an in-vitro fertilization (IVF) cycle.

Embryologist: “We will be transferring two good embryos for you.”
Patient: “I just need some more information regarding the embryos. Can I know the gender and weight of the embryos?”
Embryologist: “We can only grade the embryos as per their morphology. It is impossible for us to know the gender and weight at this stage. Also, that shouldn’t matter as long as you are having a healthy child.”