Sperm freezing has been employed for decades for male fertility preservation in cases of foreseeable or unexpected loss of fertility to guarantee future paternity, and also as a complement of assisted reproduction techniques.

Sperm quality after thawing is highly variable, even among consecutive samples from the same individual, with mean survival rates around 40%. To date, the molecular basis of the adequate resistance or intolerance to freezing/thawing protocols is unknown, and its knowledge can lead to improvement in the selection of the samples to be frozen and also in the adequate supplement of cryopreservation media. Microarray analysis provides a powerful tool to address the molecular explanation beyond this behaviour, yielding results about comparative messenger ribonucleic acid (mRNA)expression under the two different biological conditions: optimal and suboptimal survival.

Then, the aim of the investigators' study is to determine the genomic profile of sperm samples depending on their survival resistance to cryopreservation, to determine genes involved in cryodamage sensitivity.

Nested cases and controls design, with donor sperm samples frozen under conventional protocols, categorized depending on their good (GSR, n=20) (less than 20% motility decrease) or bad (BSR, n=20) (more than 20% motility decrease) survival rates. Sperm mRNA was extracted using Trizol protocol, suspended in diethylpyrocarbonate (DEPC)-treated water and frozen at -80 degrees until the microarray experiments were performed. RNAs were analyzed on Agilent Bioanalyzer 2100. Samples were pooled in 4 (5 samples/pool and 4 pools/group). Finally, 8 Agilent One colour Whole genome microarray (44K) were performed with pooled samples, 4 microarrays per group.

The results will be evaluate to detect those genes differentially expressed.

Inclusion Criteria:

The criteria used for the inclusion of donors in the sperm bank will be considered:

• males from 18 to 35 years.
• good physical and psychological conditions and no hereditary diseases
• seminal parameters: concentration > 40 million sperm / ml; percentage of progressive motility> 50% percentage of normal forms> 4%.
• For pregnancy rates after artificial insemination, only women< 40 years without tubal pathologies and artificial insemination indications will be included.

Exclusion Criteria:

All the population not included in the list of inclusion will be excluded.

Men from 18-35 years, included in the donation program of IVI Alicante. Any transmisible clinical pathology, viral infection or genetic disease should be ruled out by family history records.

In addition, seminal samples from donors must meet the seminal criteria considered by our laboratory:

• sperm concentration> 40 million sperm / ml;
• percentage of progressive motility> 50%
• percentage of normal forms> 4%.

For pregnancy rates after IUI, only women< 40 years without tubal pathologies and IUI indications will be included.