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 (PGD)

Pre-implantation Genetic Diagnosis (PGD) is a laboratory procedure, used in conjunction with IVF, which helps to reduce the risk of passing on inherited conditions.  Some of the most common reasons for PGD are specific single gene conditions (such as cystic fibrosis or sickle cell anemia) or structural changes of a parent's chromosomes. 

Typically, the couples in need of these techniques are NOT infertile. In fact, in most cases, there is a family history of the condition and the couple is seeking the opportunity to diminish the risk of having another child with significant health compromise or early death.  However, through generally available genetic screening, occasionally a couple who is seeking fertility treatment is found to be at risk of passing on an inherited condition, and PGD may become an option for them during the course of their care with us.

PGD is available for almost any inherited condition for which the exact mutation is known.  However, a unique test must usually be built for each couple who is planning to use PGD.  This test design may take up to several months to complete prior to beginning an IVF cycle. 

PGD utilizes IVF, where multiple eggs are matured and retrieved; the oocytes are inseminated with a single sperm (ICSI) and the resulting embryos are grown in culture until the 6-8 cell stage (day 3 of embryo development). 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 evaluated for the specific genetic condition anticipated.  Embryos that are determined to be unaffected are transferred back to the woman's uterus on day 5 of embryo development. 

Two main techniques are used for the genetic assessment: 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 DNA 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).

At UCSF, our embryology laboratory staff has extensive experience with embryo micromanipulation and biopsy.  Further, our genetic counselor is on staff to coordinate your cycle with the IVF team and the PGD laboratory, in order to make the process as smooth as possible.

Our genetic counselor and physicians are available to answer your questions and discuss your specific situation.  If you are interested in genetic counseling, please call Gina Davis directly at to set up an appointment.