Embryo and Semen Cryopreservation

Embryo Cryopreservation

Embryo cryopreservation or embryo freezing is a method used to preserve embryos by cooling and storing them at low temperatures. They can then be thawed at a future date and transferred to the uterus, providing additional opportunity for achieving conception.

As part of the usual process of in vitro fertilization, multiple eggs may be stimulated to grow, be recovered from the ovary and become fertilized. This may result in additional embryos in excess of the number that a couple would desire to have transferred back to the uterus at one time. If the additional embryos are of sufficiently good quality to undergo the process of cryopreservation, this can be performed in order to provide another opportunity for embryo transfer. That is, if the IVF fresh embryo transfer does not result in pregnancy, the frozen embryos can be subsequently thawed and transferred to the uterus in either a natural menstrual cycle or a hormonally-controlled cycle. Alternatively, if the IVF cycle is successful, the embryos can be stored for several years should the couple decide to attempt to have more children. UCSF will store embryos with annual renewal of a cryopreservation agreement. We have achieved pregnancies after as long as five years of storage. Success rates (pregnancies per embryo transfer procedure) are almost identical to those seen with fresh embryo transfers.

Worldwide, cryopreservation of human embryos has been shown to be a successful procedure and there are no reports of increased birth defects in pregnancies achieved through this process.

Semen Cryopreservation

Sperm from two sources can be frozen: from ejaculates or from fluid extracted in the operating room during surgical procedures (vasal, epididymal and testicular sperm specimens). The sperm is usually frozen for a period of one year; at that time, future arrangements are discussed. It is generally believed that sperm that have been through the freeze-thaw process are no more likely to result in birth defects than freshly ejaculated sperm.

Pre-Implantation Genetic Diagnosis

Preimplantation genetic diagnosis (PGD) evaluates known carriers of specific single-gene defects, such as cystic fibrosis, and parents whose offspring are at increased risk for selected chromosomal abnormalities such as Trisomy 21 (Down syndrome), Turner syndrome, and certain unbalanced translocations.

Typically, the couples in need of these techniques are NOT infertile. In fact, in most cases, the couple has had an affected child and is seeking the opportunity to diminish the risk of having another child with significant health compromise and early death.

PGD utilizes in vitro fertilization, where multiple eggs are matured and retrieved, the oocytes are inseminated with a single sperm (ICSI), and grown in culture until the 6-8 cell stage. At this point, the embryo is biopsied with the removal of 1-2 cells. This process does not damage the cells remaining within the fertilized egg. The isolated cells are then evaluated for the specific genetic defect anticipated.

Two main techniques are used for the determination: Polymerase Chain Reaction (PCR) and Fluorescent in Situ Hybridization (FISH). In PCR, multiple copies of the gene of interest are made by a process of amplification. This amplification process allows the identification of very small amounts of material in order to make the diagnosis. FISH allows the laboratory to actually count the number of chromosomes within the isolated cell. This technique is utilized primarily for expected abnormalities in chromosome number (e.g. trisomy - three copies of - 21 or Down Syndrome) or translocations (defects in the structure of the chromosome).