Rapid thawing human sperm does not affect basic parameters in normozoospermic men: a double-blind prospective study.

Purpose: To compare sperm recovery from slow versus rapid thawing technique using thirty-eight normozoospermic human sperm samples, as follows. Twentyone samples from men taking part in routine infertility screening exams (infertile group) and seventeen from proven fertile volunteer men with at least one child (fertile group).
Materials and Methods: After analysis of motility, concentration, strict morphology and functional integrity of membranes, sperm was divided into two aliquots of 0.5 mL each and frozen in TyB-G medium. Samples were thawed at room temperature (25 ± 2° C) for 25 minutes (slow thaw) or in a water bath at 75° C for 20 seconds followed by water bath at 37° C for 3 minutes (rapid thaw). After thawing, motility, strict morphology and functional integrity of membranes were evaluated by a blinded investigator. The results were expressed as mean ± standard deviation for parametric variables and analyzed using Student's t-test. Data with unpaired non-parametric variables were expressed as median (interquartile range) and analyzed by the Mann-Whitney test. Wilcoxon test was used to analyze non-parametric paired variables.
Results: There was no significant difference between techniques for total and progressive motility, percentage of normal morphological forms, hypoosmotic swelling test.
Conclusions: Although the rapid thawing protocol was completed in a shorter time (three minutes and 20 seconds versus 25 minutes, respectively), it wasn't harmful since both techniques showed comparable spermatozoa recovery. Additional research is needed to confirm its safety in clinical research before introducing this methodology in routine assisted reproduction.