A Pacific Fertility Center (PFC) patient, who underwent an embryo transfer with embryos created from vitrified and warmed donor oocytes (eggs), successfully delivered a baby in late October 2007. A healthy baby boy was born at term. Three other pregnancies are ongoing and are expected to deliver in 2008.
PFC has been developing an oocyte vitrification program for the past two years. This program is a part of their ongoing research to develop and implement new services. "Vitrification" refers to a new alternative method for freezing eggs and embryos. While it has been possible to preserve sperm for many years (the famed Dutch microscopist Antony von Leeuwenhoek allegedly cooled and then recovered sperm using snow and ice in the 17th century), reliable methods for preserving unfertilized eggs have been elusive until now.
Traditionally, preservation of sperm and embryos has been achieved with the use of a technique called slow freezing. This process incubates the sperm or embryos in low concentrations of cryoprotectants (antifreeze) to draw water out of the cells, which are then cooled very slowly to sub zero temperatures. This technology typically only works for cells that exist individually or in small numbers, such as sperm and embryos. However, slow freezing does not work well for human eggs. In fact, the estimates for rates of success with slow freezing is about two births for every 100 eggs thawed.
In recent months, this vitrification technology has been used at PFC for oocyte preservation. Vitrification works by using higher concentrations of cryoprotectants and much faster cooling rates. Cells are cooled in tiny straws which achieve cooling rates of several thousand degrees per minute. When vitrification straws and cryoprotectants were first approved by the FDA for human embryos, PFC began the process of adapting the technology to oocytes. "Even though we've been handling oocytes and embryos for many years, this technology provided new challenges due to the tiny size of the straws and the speed at which they had to be cooled," says Joe Conaghan, Ph.D., HCLD, Laboratory Director and Embryologist at PFC. "Once proficient with the procedure, we began to freeze high quality oocytes from donors that had proven fertility. Using these quality oocytes, we could be assured that any failure would be the result of the vitrification technology and not the oocytes."
Five oocyte donors in their twenties were recruited and all of their oocytes were vitrified immediately after their oocyte retrieval procedures. The oocytes were then offered to specific PFC patients waiting for donated embryos. The immediate availability of the vitrified oocytes and the ability to choose the sperm source made this a great alternative to accepting donated embryos.
PFC had immediate success with the first recipient. "We had vitrified 16 oocytes from the first donor. For the first recipient we warmed only 7 of these," explains Dr. Conaghan. "Four hours later we injected a single sperm into 6 oocytes that survived the vitrification process (1 oocyte had not come through the process successfully). The next morning, 3 of the oocytes had fertilized. Two days later, 3 embryos were transferred. A positive pregnancy test and ultrasound confirmed a singleton pregnancy. This success was a great reward for our efforts."
Overall, PFC had 7 out of 10 embryos implant after transfers to 6 recipients. What is very exciting is that this implantation rate (70%) is comparable to the implantation rates seen with donor oocytes which have not been cryopreserved. While these results are encouraging and have brought great joy to a small number of patients, there are more issues to resolve before the center declares complete success. "The 70% success rate was obtained with the use of the highest quality oocytes from young donors in their 20's who were known to be fertile and healthy. However, we also had 2 donors that produced poor quality oocytes that did not survive the vitrification procedure," says PFC reproductive specialist Carl Herbert, M.D. He adds, "We are uncertain how results may vary using oocytes from women in their late 30's. As age is a prominent factor in fertility success, obviously there will be differences in the outcome. We are currently creating a protocol that will address this issue."
PFC offers oocyte vitrification unconditionally to unmarried young women with cancer whose treatments may render them sterile. In the future, oocyte vitrification may be a possible option for women who need or wish to delay child bearing. However, until there are more data with oocytes from a variety of women, PFC is being very careful about offering vitrification routinely to women who are worried about the biological clock. That said, PFC reproductive specialist Carolyn Givens, M.D. reveals, "We are currently planning a study in women in their mid- to late thirties to vitrify and warm their eggs in order to determine whether or not rates of egg survival will be comparable to those we are experiencing with young and healthy donor eggs. If we see rates of conception with transfer of embryos from vitrified eggs in our thirty-something year-old patients that are comparable to the rates we would expect with embryos that had never been cryopreserved, we would expect to offer this technology as one of our services."
About Pacific Fertility Center
Pacific Fertility Center (PFC) is a fertility medical practice and egg donor agency located in San Francisco, California. PFC physicians are board certified by the American Board of Obstetrics and Gynecology in Reproductive Endocrinology and Infertility. The physicians at PFC are members of the Society of Assisted Reproductive Technology (SART); Society of Reproductive Endocrinology and Infertility (SREI); and the American Society of Reproductive Medicine (ASRM). They each have many years of successful clinical, academic, and scientific experience.