There used to be a time when we would transfer only fresh embryos routinely in all IVF cycles. After egg collection, the fresh embryos would be transferred back into the uterus in that cycle itself – either on Day 3 or Day 5. Today, however, the standard practice is to freeze all embryos on Day 5 ( blastocysts) and then transfer these frozen embryos after thawing them in subsequent cycles.

Patients often wonder why we do, this because this increases the time they take to get pregnant, as they have to wait an additional month for their transfer.

This is the reason why this has become routine in all good IVF clinics across the world.

Remember that the chances of pregnancy depend on two independent variables. The first is the quality of the embryos, and the second is endometrial receptivity. When we do an IVF cycle, our focus is on creating good-quality embryos by superovulating the patient, we can retrieve lots of good-quality eggs. However, the problem is that the hormones used for superovulation often cause impaired endometrial receptivity , as a result of which even a good-quality embryo will not implant in an unfavorable uterine lining.

This is why we now break up IVF treatment into two different legs. In the first half, we concentrate on producing good quality embryos by optimizing the superovulation protocol so we can collect many good quality eggs, without worrying about the effect of these hormones on endometrial receptivity – after all, it’s hard to have your cake, and eat it too!

Once we have created good-quality embryos, we freeze them. Then in the next cycle, we concentrate on improving endometrial receptivity, and since we no longer need to grow eggs anymore, we have already frozen the embryos.

We can now transfer these top-quality embryos into an optimally prepared uterine lining, which means the chances of the embryo implanting is far better.

This has become a reality today because embryo freezing using vitrification has become such a robust procedure, that survival rates are practically 100% in good clinics like ours.

Another advantage of this protocol is that the risk of OHSS (ovarian hyperstimulation syndrome) goes down dramatically, because we don’t do a fresh transfer.