Dr. Hammitt has published numerous scientific articles over the last twenty years on embryo cryopreservation, or the freezing of embryos. The IVF laboratories she directed at the Mayo Clinic from 1992 through 2005 were national and world leaders in embryo cryopreservation. More than 60 percent of patients entering the Mayo Clinic IVF program had extra embryos available for freezing because of a unique method of grading and selecting the best embryos for fresh embryo transfer and freezing the remaining embryos for later use. The frozen-embryo transfer (FET) pregnancy rate achieved over a 10-year period of using this method was over twice the national average. A frozen embryo transfer is much less costly and less invasive than an egg retrieval. This high pregnancy rate with frozen embryos allows couples to have a greater than 65 percent chance of pregnancy from one egg retrieval or egg harvest procedure. High success rates with frozen embryos lowers the overall cost of infertility treatment and the time away from work for couples to achieve their goal of conception and delivery of a healthy baby.
To decrease the likelihood of multiple pregnancy, it is important to limit the number of embryos transferred in each treatment cycle. High success rates with frozen embryos permits transfer of fewer embryos in the fresh retrieval cycle without wasting the nontransferred embryos. In general women under 30 should have only one or two embryos transferred per treatment cycle. Women 30-35 should have no more than two to three embryos transferred. Women over 35 should usually have no more than three to four embryos transferred. Restricting the number of embryos transferred in this manner decreases the incidence of high-order multiple pregnancies, that is triplets or more. Limiting the incidence of high-order multiple pregnancies is important to protect the health of the mother and babies born from Assisted Reproductive Technology (ART) procedures.