Liquid nitrogen vapor is comparable to liquid nitrogen for storage of cryopreserved human sperm: evidence from the characteristics of post-thaw human sperm

OBJECTIVE

To compare the differences in the characteristics of post-thaw human sperm after storage in either liquid nitrogen (LN2; -196 °C) or LN2 vapor (-167 °C).

DESIGN

Experimental study.

SETTING

University hospital.

PATIENT(S)

Thirty healthy volunteers who agreed to donate their normal semen samples for infertility or research were included in the study.

INTERVENTION(S)

Semen samples (n = 30) were divided into eight aliquots and frozen. Four aliquots of each human semen sample were stored in LN2 (-196 °C), and the other four aliquots were stored in LN2 vapor (-167 °C). After 1, 3, 6, or 12 months, samples were thawed and analyzed.

MAIN OUTCOME MEASURE(S)

The motility was evaluated by the manual counting method. The viability was estimated by eosin staining. The morphology was analyzed by Diff-Quik staining. The sperm DNA integrity was determined with acridine orange fluorescent staining, and acrosin activity was assayed by the modified Kennedy method.

RESULT(S)

The characteristics of post-thaw human sperm, including motility, viability, morphology, DNA integrity, and acrosin activity, showed no significant difference between LN2 and LN2 vapor storage for the different time periods.

CONCLUSION(S)

LN2 vapor was comparable to LN2 in post-thaw sperm characteristics, suggesting that LN2 vapor may be substituted for LN2 for the long-term storage of human sperm.

Optimizing human semen cryopreservation by reducing test vial volume and repetitive test vial sampling

OBJECTIVE

To investigate optimal test vial (TV) volume, utility and reliability of TVs, intermediate temperature exposure (-88°C to -93°C) before cryostorage, cryostorage in nitrogen vapor (VN2) and liquid nitrogen (LN2), and long-term stability of VN2 cryostorage of human semen.

DESIGN

Prospective clinical laboratory study.

SETTING

University assisted reproductive technology (ART) laboratory.

PATIENT(S)

A total of 594 patients undergoing semen analysis and cryopreservation.

INTERVENTION(S)

Semen analysis, cryopreservation with different intermediate steps and in different volumes (50-1,000 μL), and long-term storage in LN2 or VN2.

MAIN OUTCOME MEASURE(S)

Optimal TV volume, prediction of cryosurvival (CS) in ART procedure vials (ARTVs) with pre-freeze semen parameters and TV CS, post-thaw motility after two- or three-step semen cryopreservation and cryostorage in VN2 and LN2.

RESULT(S)

Test vial volume of 50 μL yielded lower CS than other volumes tested. Cryosurvival of 100 μL was similar to that of larger volumes tested. An intermediate temperature exposure (-88°C to -93°C for 20 minutes) during cryopreservation did not affect post-thaw motility. Cryosurvival of TVs and ARTVs from the same ejaculate were similar. Cryosurvival of the first TV in a series of cryopreserved ejaculates was similar to and correlated with that of TVs from different ejaculates within the same patient. Cryosurvival of the first TV was correlated with subsequent ARTVs. Long-term cryostorage in VN2 did not affect CS.

CONCLUSION(S)

This study provides experimental evidence for use of a single 100 μL TV per patient to predict CS when freezing multiple ejaculates over a short period of time (<10 days). Additionally, semen cryostorage in VN2 provides a stable and safe environment over time.