A bridge to intracytoplasmic sperm injection--high insemination concentrations benefit patients who have a reduced chance of fertilization with standard in-vitro fertilization.

This study was carried out to determine whether high insemination concentrations (HIC) could improve fertilization and pregnancy rates in patients who had either previously demonstrated poor fertilization rates in vitro using standard protocols (Group 1) or in whom a reduced chance of fertilization was indicated at semen assessment prior to in-vitro fertilization (IVF) (Groups 2 and 3). Forty nine patients were recruited for the study. Standard IVF was carried out in 1 ml volumes using 10(5) spermatozoa/ml. HIC treatment involved co-culture of spermatozoa and oocytes in microdroplets with insemination concentrations increased 10-50 fold higher than standard IVF. Fertilization and pregnancy rates were compared between standard IVF and HIC in individual patients either in consecutive cycles (Group 1) or using sibling oocytes in the same cycle (Group 2). Group 3 patients were treated with HIC for their first treatment cycle. HIC significantly improved the fertilization rate compared with standard IVF for Groups 1 (59.7 +/- 10.7 versus 19.6 +/- 5.4% respectively) and 2 (54.9 +/- 8.5 versus 34.0 +/- 8.5% respectively). HIC increased the pregnancy rate from 0% with standard IVF to 20% per embryo transfer in Group 1 patients. A single pregnancy derived from the transfer of HIC and IVF embryos occurred in Group 2. The fertilization rate (47.2 +/- 7.6%) and pregnancy rate (31.3% per embryo transfer) for Group 3 patients was higher than predicted. There was no increase in the rate of polyploidy with HIC. Provided there are sufficient numbers of motile spermatozoa, HIC may be offered as an initial form of treatment, thus permitting referral of only the poorest responders for intracytoplasmic sperm injection (ICSI).