People often have questions about how many sperm should be in a vial and how this count is determined.
Total Motile Sperm After Thawing
*The number of motile sperm in a sample is determined by an estimation method taken from a representative drop of the sample. The estimation in quantity of total motile sperm can range up to 30% based on inherent qualities of this biologically active sample, and variation in methods used to derive count, motility and volume recovery. It is expected that the values obtained by your laboratory fall within 30% of our total motile target concentration.
Amount of sperm needed to achieve pregnancy
Numerous studies find that pregnancy rates with intrauterine insemination (IUI) are maximized with 5 million total motile donor sperm (In fact, more recent studies suggest that outcomes are maximized with much less donor sperm). In other words, the chances of a successful pregnancy via IUI do not increase with more sperm. California Cryobank has established vial standards that well-exceed the number of sperm required to maximize the chance of achieving pregnancy.
Amount of sperm in ICI and IUI vials
The California Cryobank vial standards refer to the total motile sperm in a vial. The total motile count is calculated by multiplying the percentage of all motile sperm by the total number of sperm counted.
We target post-thaw counts of 15 million and 10 million total motile sperm in our ICI and our IUI vials, respectively. Vial counts will predictably fall within a range of plus or minus 30% from the target value. This means that after thaw, an ICI vial will produce counts between 10.5 and 19.5 million total motile sperm, and an IUI vial will produce counts between 7 and 13 million total motile sperm. ICI counts should always be performed prior to a wash. No wash is necessary for IUI vials.
As one of our many quality control procedures, we perform a post-thaw count on one vial from every lot created to confirm the sperm survive the freezing process and the vials meet our high standards.
Why provide a range for the number of total motile sperm in our vials?
Quantifying sperm is quite unlike counting the contents of a medicine bottle. The number of motile sperm in a sample is determined by an estimation method taken from a representative drop of the sample. Sperm are living, moving cells, and under the best of circumstances the estimation of total motile sperm can vary by 30%.
There are three components, all of which have associated sources of variation, that factor into the calculation of total motile concentration in a sperm vial:
In addition to variation inherent to a moving biological sample, variables such as individual technician thawing and counting technique, sample homogeneity, and the type of counting chamber used can significantly affect the estimated sperm count. For example, CCB uses a device called a Makler chamber to count sperm under a microscope. This counting chamber has a large depth of field that allows technicians to evaluate a three-dimensional drop of sperm. Many clinics use a system that relies on disposable slides. Disposable chambers sandwich a drop of the specimen between two slides, pushing much of liquid to the edges. While these slides are a perfectly acceptable means for evaluating a sperm sample, they are known to produce counts that are on average 30% lower than those derived from the Makler chamber. One must make an adjustment for this difference into consideration when comparing calculations based on the disposable slides to those produced using a Makler chamber.
Normal motility for a previously frozen sperm sample is any fraction between 20% and 40%. As with count, different laboratories will produce very different estimations of motility based on the mechanism used to thaw, the amount of time the specimen is allowed to thaw, and the counting chamber used.
Occasionally physicians’ laboratories factor sample volume into their assessment of vial contents. Our laboratory uses calibrated instruments to precisely deliver an exact volume of sample in every vial. We deliver at least 0.5mL and 1.0 mL into IUI and ICI vials, respectively. A variety of different means may be employed to recover the specimen from the vials. It’s not unusual for minute amounts of residual specimen to cling to the side of a cryovial or the underside of a cryovial lid. For these reasons, measurement of recovery volume is often an estimation and should not be factored into the determination of total motile sperm count in a vial. One can expect to recover a range of volumes between 0.4 to 0.5 mL for IUI vials and 0.8 to 1.0 mL for ICI vials. For the purposes of calculating total motile sperm per milliliter, we recommend the use of 0.5 mL for IUI vials and 1.0 mL for ICI vials, based on the calibrated volume that is delivered in our laboratories.