The impact of a modification of the intracytoplasmic sperm injection (ICSI) technique on fertilization and pregnancy rates was examined in a retrospective analysis of 171 consecutive ICSI treatment cycles (156 patients). Patients were selected for ICSI on the basis of severe oligoasthenozoospermia (65 patients) or following conventional in vitro fertilization (IVF) with failed or poor fertilization (70 patients). Seven patients in which epididymal or testicular sperm was used, 10 patients with sperm antibodies and 4 patients with retrograde ejaculation or who required electro-ejaculation were also treated with ICSI. In the first 105 cycles (102 patients), single sperm, rendered immotile, were injected into the ooplasm of 979 metaphase II (M II) oocytes using an established technique (Method 1). In the following 66 cycles (513 M II oocytes injected), the ICSI procedure was modified by increased aspiration of the oolemma to ensure the intracytoplasmic deposition of sperm (Method 2). The patient groups did not differ between the two injection procedures. The normal (two pronuclear) fertilization rate increased significantly (P <0-001) from 34-3% with Method 1 to 73-1% with Method 2, with no difference in the oocyte degeneration rate (4-3% v. 4-5% respectively). The incidence of failed fertilization was significantly (P <0-01) reduced from 17-1% (18 cycles) to 1-6% (1 cycle) with the change in technique. As a consequence of the increased fertilization rates with Method 2, more embryos were available for assessment and transfer, and a pregnancy rate per oocyte retrieval of 21 • 2% was obtained for Method 2. Fertilization, embryo transfer and pregnancies were obtained in all patient groups treated with ICSI. To date, 8 normal children (including one set of twins) have been born. It is concluded that an optimal injection procedure is essential for the success of the ICSI technique.
- Male infertility