Abstract:

Objective To explore sperm cryopreservation in capillary by ultra-rapid procedure, and seek an optimal method to cryopreserve small numbers of human spermatozoa. Methods Twenty semen samples from 20 healthy donors were selected from Shanghai Human Sperm Bank. Each sample was divided into 4 groups for cryopreservation after dilution to the density of （3-5）×10⁶/mL (3-5/high power filed). In group A, samples mixed with sperm freezing medium in 0.5 mL straw were frozen by program procedure. In group B, samples mixed with sperm freezing medium in capillary were frozen by program procedure. In group C, samples mixed with modified glycerol-yolk-citrate (GYC) in capillary were frozen by program procedure. In group D, samples mixed with modified GYC in capillary were frozen by direct liquid nitrogen vapor method with ultra-rapid speed. The post-thaw viability rates and normal morphology rates were compared among groups. Results The pre-thaw viability rate of the 4 groups was (68.6±21.3)%, and the post-thaw viability rates of group A, B, C and D were (32.2±17.2)%, (41.5±18.4)%, (44.9±18.0)% and (50.2±19.7)%, respectively. The post-thaw viability rates of group B, C and D were significantly higher than that of group A (P<0.05), and the post-thaw viability rate of group D was significantly higher than those of the other 3 groups (P<0.05). There was no significant difference in the post-thaw normal morphology rates among group A, B, C and D [(14.2±4.1)%, (15.0±4.7)%, (14.5±5.2)% and (15.9±4.9)%, respectively, P>0.05]. Conclusion Ultra-rapid freezing with direct liquid nitrogen vapor in capillary is an optical method for cryopreservation of small numbers of human spermatozoa, which may yield high recovery rate. Modified GYC has the same cryoprotecting effect as sperm freezing medium.

Key words: spermatozoa, cryopreservation, recovery rate, ultra-rapid cryopreservation