The process of cryopreservation allows you to store embryos for future use. During an IVF cycle, several eggs will be retrieved and fertilized (through ICSI). We fertilize extra eggs, because not all of the fertilized eggs will successfully develop into healthy embryos. Because the goal of IVF treatment is a singleton pregnancy (only one baby at a time), we will only transfer between one and four embryos into the mother’s uterus, with the exact number transferred depending on several factors.
If there are healthy embryos left that weren’t transferred, they can be frozen for future use. If the couple chooses to try for another pregnancy, the embryos can be unfrozen and then transferred into the mother’s uterus, avoiding the need for another cycle of ovulation induction, egg retrieval, and fertilization.
In some cases, the uterine lining is not receptive enough to transfer fresh embryos that were created during that cycle. In this case, we will freeze all of the healthy embryos, and later unfreeze them for transfer. At our fertility clinic in Tucson, we will only transfer fresh embryos if the uterus is receptive and a pregnancy is likely; otherwise, we freeze them and save them for another cycle, to give the best chance of success.
How Do Frozen Embryo Transfers Work?
We culture all embryos to the blastocyst stage, or day five of embryonic development. In a typical in vitro fertilization cycle, between three and eight blastocysts are typically produced. Blastocysts have very small cells and freeze and thaw with a 95 percent survival rate. The embryos are frozen individually, allowing them to chromosomally tested and then used later, one at a time.
Preparation of the uterine lining for frozen embryo transfer is simple. We typically use a pill form of estrogen to encourage the uterine lining to proliferate. Then, on about the 14th day of the protocol, we begin adding progesterone. The thawed blastocysts are transferred on the 6th day following the start of progesterone.
Why are Frozen Embryo Transfers Necessary?
At our fertility clinic near Glendale, most of our in vitro fertilization cycles do not have a fresh embryo transfer because the uterine lining is not as receptive as we would like it. High levels of estrogen, hyper-stimulation syndrome, uterine polyps or fibroids or endometrial linings that are too thin or too thick will prevent the fresh transfer from occurring. In these cases, the blastocysts are cryopreserved and we work on making the uterine lining receptive. Once any lining issues have been corrected, we prepare the embryos for transfer.
Success of Frozen Embryo Transfers in Tucson
There was a time when frozen embryos were not as successful at producing pregnancies as “fresh” embryos. With improved laboratory techniques, and with the focus being on the receptivity of the uterus, the rates of pregnancy between frozen embryos and fresh embryos favor the frozen embryos.
Embryos can be stored in liquid nitrogen for decades without harm. There has not been any data showing that previously frozen embryos have more birth defects or genetic disease than do fresh embryos. Billing for storage of frozen embryos occurs annually.