A. The process -
ust as each person is unique, so is the success of the freezing/thawing process
for each sperm sample. For each semen sample we determine the semen volume, sperm
count (concentration), and percent motility (number of sperm that swim). We use
a special solution (cryoprotectant) to protect the sperm from freezing conditions
and place it into distinctive containers (cryovials) for freezing. Depending on
the size and the quality of the sample, we will use one or more vials per sample.
(Each vial can hold up to 1.8 ml). Each vial is labeled with your name, the freeze
date and a unique vial number. The vials are slowly cooled, then frozen and stored
in our liquid nitrogen tanks. Following freezing of the first sample, a small volume
of semen is thawed to determine how well the freezing process worked and the number
of motile sperm remaining per vial.
B. How Cryopreservation is Performed -
After a semen sample has been collected, it is placed on a warming block maintained
at 37°C, to liquefy. At this time, the semen sample is mixed in a 1:1 ratio with
a freezing medium that allows the sperm to survive the freezing and storage process.
The semen and freezing medium mixture is divided up into one milliliter portions
and placed in special containers called cryovials. The freezing medium used contains
cyroprotectants. Cryoprotectants are chemicals that help remove water from the cells
being frozen. If the water is not removed from the sperm, ice crystals will form
inside of the cell and break up it up, resulting in cell death.
Semen samples are slowly frozen in liquid nitrogen vapors. Once the samples have
been frozen in the liquid nitrogen vapors, they are placed in special containers
where they are stored in the liquid nitrogen until they are needed. There is a considerable
amount of variability, but each ejaculate typically yields from one to six vials.
Each vial of a patient’s semen sample is labeled with the patient’s name, the date,
and a unique number recorded on the side. This information will be used to catalog
the semen sample into the storage facility.
C.Test Thaw Procedure
The survival rate of sperm after cryopreservation is highly variable. In situations where
loss of a small portion of the semen is not critical, it is recommended that one of the
cryovials be thawed to assess how successfully an individual’s semen can be stored and thawed.
D. Success rates with frozen sperm
If you choose to have your sperm frozen, you can use your sperm at a later date to get pregnant.
This would work either through intrauterine insemination (IUI) or in vitro fertilization (IVF).
When we thaw the sperm sample, experts in our lab are able to analyze the motility (ability to move)
and mobility of the sperm through a “test thaw.” If the sperm has been negatively affected by
freezing/thawing, the rate of conception through IUI may be lower. When we identify poor
sperm characteristics, or when very few frozen sperm samples are available, IVF may be a better
choice. In general, the IVF success rate is not affected by using cryopreserved semen.
In any event, when the time comes, you will always have the opportunity to discuss options with
one of our specialists. We will help you determine the best options for achieving a pregnancy
using your frozen samples.
E. The number of semen samples to freeze
When it’s time to decide how many samples to freeze, you will work with your doctor and discuss:
- 1. Semen quality.
- 2. Conception rates
- 3. Current technology.
- 4. Anticipated sample need.
- 5. Time constraints.
Regardless of how many samples are frozen, sperm cryopreservation does not guarantee
future reproductive success. However, the goal is always to preserve a reasonable chance at
producing a pregnancy.
We recommend that enough samples are frozen (cryobanked) to provide thawed sperm for at
least four intrauterine inseminations IUIs. And that each of these contain at least 10-20
million motile sperm each. The number of samples needed to achieve this standard is totally
dependent on the sperm count and motility of each ejaculate. A typical man can achieve this
level by freezing two semen samples. If your sample does not meet this standard, you may
still effectively use IVF. It is possible, that you may not have enough time to freeze
multiple samples before undergoing their medical treatments. Our lab can provide the
cryopreservation data to your doctor. We will indicate whether additional freezing is recommended.
F. Length of time sperm samples may be frozen
As far as we know, the viability of cryopreserved sperm may be kept forever.
This is due to the freezing technique and because the semen is stored at such a
low temperature (-196 C). Samples stored more than 20 years have been used to
create successful pregnancies and healthy babies.