It is not possible to predict with certainty which oocytes (eggs) will fertilize and form preembryos (fertilized eggs) or blastocysts (an advanced stage of development of the preembryo-usually on day 5-6). Therefore, when normal appearing oocytes are fertilized, sometimes more preembryos/blastocysts will form than should safely be placed into the uterus. In anticipation of “extra” preembryos/blastocysts, couples must decide what to do with them.
Preembryos/blastocysts are “graded” prior to selection for transfer to the uterus. Grading preembryos is an evaluation initially performed in the ART laboratory on the second day after the egg and sperm have been united. Blastocysts are graded usually on day 5 or 6. The laboratory staff evaluates the embryos under the microscope for quality. This evaluation is based on standardized laboratory assessment criteria that include cell shape and size. The preembryos/blastocysts are not being evaluated for genetic characteristics.
The preembryos/blastocysts selected for transfer during the initial or “fresh” cycle are the highest in quality, or grade, since this is the cycle with the optimal chance for pregnancy. There are several options available for high quality blastocysts in excess of those transferred to the uterus or tubes.
- Cryopreservation (freezing) of blastocysts.
- Disposal of preembryos/blastocysts according to the ART Program’s practices and procedures at that time.
- Use of the preembryos/blastocysts for scientific education or research, followed by disposal.
- Donation of the preembryos/blastocysts to another infertilie couple, if a couple is available. (This option requires an additional consent form and advanced planning for coordination with another couple. It assumes that the donating couple is available for testing at the time of donation. i.e., HIV testing. It also assumes that the preembryos/blastocysts are desirable in terms of egg and sperm quality, i.e., age less than 35).
Couples must make their choices in writing, in advance of the ART cycle, when they sign their consent forms with their physicians. Although only 35% of couples will produce enough high quality embryos to be able to cryopreserve, it is probably better for couples to assume that they will have additional blastocysts, and if so, what would they want to do with them.
Blastocysts can be cryopreserved and transferred in a subsequent cycle should pregnancy not occur in the initial cycle. They may also be used to establish a sibling pregnancy at a later time if pregnancy occurs initially. Once cryopreserved, the viability of the preembryos/blastocysts is generally not thought to decline even after years of storage. However, we encourage couples to use them for transfer or decide on disposal within a reasonable time. One year is the original storage agreement.
Some or all of the preembryos/blastocysts may not survive cryopreservation and thawing. Nationally, about 60% survive, however, newer cryopreservation techniques have resulted in significantly higher rates of thawed embryo survival.
There does not appear to be an increased risk to the fetus by embryo cryopreservation and thawing, but it cannot be quantified with certainty until more live births result from cryopreserved preembryos/blastocysts.
Our current recommendation is to only cryopreserve blastocysts that are “Grade I” or higher quality “Grade II”. We believe the lesser grade preembryos/blastocysts are less likely to survive the thaw, or, if they survive the thaw, less likely to result in pregnancy.
Some factors to consider when deciding whether or not to cryopreserve preembryos/blastocysts include:
A. Expenses involved in cryopreserving and storing preembryos/blastocysts.
B. Costs of a cryopreserved frozen embryo transfer cycle are significantly less than a “fresh” cycle.
C. Pregnancy rates of a cryopreserved preembryos/blastocysts replacement cycle are somewhat lower than a “fresh” cycle.
D. Not all preembryos/blastocysts survive the cryopreservation and thaw process (possibly none may survive).
If a couple has strong religious or moral beliefs that lead them to cryopreserve all preembryos/blastocysts, regardless of their grades, or which prevent them from choosing the other 3 options described above; those couples may direct us to cryopreserve all preembryos/blastocysts regardless of their grades.
Couples who store cryopreserved preembryos/blastocysts have an obligation to notify their physician and the ART program in writing of any change in their address. Additionally, there is a fee associated with the cryopreservation and storage of preembryos/blastocysts. If a couple pays for cryopreservation but then does not have enough preembryos/blastocysts available for cryopreservation to be performed, the couple will receive a refund in the amount paid for cryopreservation. Unforeseen increases in the cost of cryopreservation may dictate an increase in couples storage costs.