Again, the higher success rates will be largely attributed to the patient population. Pregnancy rates, especially in the younger population, are very dependent upon the number of embryos or eggs transferred. The policies for fresh embryo transfer and embryo cryopreservation are very different among clinics and greatly influence the pregnancy rates. Many programs freeze some of the pre -embryos at the pronuclear stage. There are many advantages to freezing excess embryos including additional future embryo transfers without repeating drug stimulation and egg retrieval.
Many patients undergo multiple cycles using their cryopreserved embryos at greatly reduced cost.
Controlling the number of embryos transferred also reduces the incidence of multiple pregnancies. The clinic's 1999 data is likely to be very different than the 1997 SART data. For example, a clinic that had poor results with ICSI in 1996 may have much better results in 1999. Technology evolves very rapidly in the field of reproductive medicine and the SART data is dated. These are many additional reasons that make clinic comparisons utilizing the SART data suspect.