AGGRESSIVE SPERM IMMOBILIZATION PRIOR TO INTRACYTOPLASMIC SPERM INJECTION WITH IMMATURE SPERMATOZOA IMPROVES FERTILIZATION AND PREGNANCY RATES

This study was conducted to determine whether the mode of sperm immobi lization prior to intracytoplasmic sperm injection (ICSI) influences f ertilization by immature spermatozoa. Of the 837 ICSI cycles evaluated , 81 were performed with epididymal or testicular spermatozoa; 35 cycl es with epididymal spermatozoa immobilized in the standard fashion res ulted in fertilization and pregnancy rates of 48.3 and 51.4% respectiv ely. When a more aggressive sperm immobilization technique (i.e. perma nently crimping the sperm flagellum between the midpiece and the rest of the tail) was applied in 17 cycles, the resultant fertilization and pregnancy rates were significantly (P < 0.05) higher: 82.0 and 82.4% respectively. Similar increases in fertilization and ensuing pregnancy rates were also observed in ICSI cycles with the aggressive immobiliz ation of frozen-thawed epididymal spermatozoa (eight cycles) versus st andard immobilization (16 cycles). However, the fertilization rates fo r ICSI using testicular spermatozoa (five cycles) were basically the s ame, regardless of the immobilization technique. Furthermore, for ejac ulated spermatozoa (756 cycles), the fertilization rates following agg ressive sperm immobilization were also positively affected (73.4%), al though no statistical differences in the clinical pregnancy rates were found. Because aggressive immobilization appears to affect sperm memb rane permeabilization, the enhanced fertilization patterns observed in immature spermatozoa following aggressive immobilization may suggest a different membrane constitution in these spermatozoa. These findings indicate that immature gametes may require additional manipulation to enhance the post-ICSI events essential for adequate nuclear decondens ation.