Advantages of Embryo Freezing
Recently published studies have suggested that there may be previously unappreciated advantages associated with transferring frozen thawed embryos compared to transferring embryos in the fresh cycle. It has long been recognized that the controlled ovarian stimulation usually used for fresh IVF treatment cycles results in very high estrogen levels and acceleration of uterine lining maturation. It has also been accepted that transferring frozen embryos results in lower live birth rates due to detrimental effects of freezing on the integrity of the embryo. The conventional wisdom has been that any advantages gained by not transferring the fresh embryos into the overly stimulated uterine lining would be offset by the decreased in live birth rate associated with transferring frozen, thawed embryos.
However, recent studies have indicated that when the best embryos produced in an IVF treatment cycle are frozen and later transferred in a cycle in which there is no controlled over-stimulation of the ovaries and therefore normal amounts of estrogen preparing the uterine lining for embryo attachment, higher live birth rates may be achieved. In addition, frozen/thawed embryo transfer cycles have lower tubal pregnancy rates. This lower tubal pregnancy rate may have something to do with increased uterine contractions caused by high estrogen levels in fresh IVF treatment cycles although this has not been proven. Additionally, not transferring embryos in the fresh IVF treatment cycle dramatically reduces the incidence of ovarian hyperstimulation syndrome, a potentially life threatening condition. When embryos are transferred in the fresh stimulated cycle, the presence of HCG (human chorionic gonadotropin) which is secreted by the implanting embryo has a stimulatory effect on the already quite stimulated ovary resulting in the ovarian hyperstimulation syndrome. The ovary is not stimulated in the frozen embryo transfer cycle and therefore estrogen levels are relatively normal, and hyperstimulation does not occur.
If additional studies support these recent findings, we may see a significant change in how we conduct IVF treatment cycles. Stimulating the ovaries and retrieving eggs would be done in one cycle with freezing of all eligible embryos shortly after fertilization. The patient would then await the onset of menstruation, and then go through a controlled, planned frozen embryo transfer cycle. Improved live birth rates, reduced tubal pregnancy rates, and elimination of ovarian hyperstimulation syndrome may prove to be impressive advantages of this approac