Increasing sperm concentration to adjust for subnormal sperm morphology did not adversely affect implantation after embryo transfer.

Some sperm specimens contribute to infertility not by impairing the fertilization process but by causing embryo implantation defects. One hypothesis is that a toxic factor attached to the sperm is transferred to the zona pellucida by the supernumerary sperm and then subsequently to the embryo membrane. One abnormality, as manifested by subnormal hypoosmotic swelling test (HOST) scores, causes these problems even with the small number of sperm that attach to the zona pellucida under normal physiologic conditions. This study evaluated whether the technique used to increase the oocyte insemination concentration of sperm to adjust for subnormal morphology values using strict criteria may allow a higher concentration of this purported toxic factor to attach to the zona pellucida, thus resulting in the dissimilitude of normal fertilization rate but low implantation rate. A comparison of the pregnancy and implantation rate of embryos formed by insemination of this adjusted sperm concentration of < or = 200,000 sperm vs. those inseminated with the normal concentration of 25,000 sperm failed to demonstrate any differences. Thus, the technique of increasing sperm concentration to adjust for low sperm morphology to improve fertilization rates does not seem to adversely affect implantation rates as long as the HOST scores are normal.