Conventionally Fresh Embryo Transfer in an IVF or ICSI cycle was done on Day 3 or Day 5 after OPU (OPU – Ovum Pick Up day is considered Day 0). This is known as a Fresh IVF ET Cycle.
Another viewpoint is that the environment of the uterus is not suitable for Embryo Transfer in a stimulated cycle. This is because the hormone levels in a stimulated cycle are very high and unnatural as compared to a natural cycle. Such high levels of hormone (Estrogen) are not good for implantation, because of which success rates in a stimulated cycle is less. In short, Ovarian Stimulation has an adverse impact on implantation rates in IVF / ICSI cycles.
Studies suggest that the modifications in uterine environment that occurs during a Controlled Ovarian Stimulation (Stimulation to ovaries using drugs to produce follicles), may be detrimental to the IVF outcome after Fresh Embryo Transfer compared to a Frozen Embryo Transfer cycle.
In older days where the cryopreservation of embryos was not as robust, clinicians were apprehensive of cryopreserving good embryo’s hence wanted to transfer them in a fresh IVF ICSI cycle. However in the past few years we have seen significant improvement in both Cryopreservation media and protocol, resulting in nearly 100% embryo and oocyte survivability. This has given confidence to Infertility Specialists and today, most of the clinician’s prefer a Freeze All IVF Cycle for their patients.