In Vitro Fertilization (IVF)

Candidate Embryos

embryo transfer

Equal amounts of research and consternation center on the proper cultivation, collection and treatment of oocytes during the IVF cycle. Only mature oocytes are a candidate for fertilization.  Moreover, only a minor percentage of fertilized eggs will be candidate embryos for transfer. And now of these candidate embryos, a fraction of them harbor normal genetics and, when implanted, result in babies. The focus is on the oocyte-sperm, embryo unit.

However, the data is clear. Even the most normal of embryos (ones that have even tested to harbor normal chromosomes) have a an approximate 70% pregnancy rate (and a small miscarriage rate). We must now turn our attention to what can become the “rate-limiting step”, the bottleneck in implantation; and it may rest in the endometrium.

The window of implantation is a mere 24 hours, approximately. It coincides with the 5th-6th day of embryo growth where the embryo is hatching out of its protective shell. The parallel protective coating of the endometrium dissolves and then becomes receptive to the embryo. Together, receptors on the endometrium and the embryo come together and the implantation process begins. A similar protective coating returns to the endometrium preventing further implantation events.

But what if that window is shifted either earlier or later? It can be easily imagined that the embryo would simply bounce again and then dissolve. Most endometrium are expected to be ready when the embryo is ready (>80%). However, there are a subset of endometrium that may not ready. These are the women that have undergone multiple IVF cycles with either biochemical pregnancies or no pregnancies at all.

To this end exists a diagnostic test to detail the window of implantation. It is termed an endometrial receptivity test (ERA). Basically, there is a genetic footprint of the implantation window. The test requires an endometrial biopsy at the time of anticipated embryo implantation.  This biopsy is then processed and the genetic profile is determined to verify the implantation window.

If you would look to learn more about the ERA test, please contact us!