Effect of treating sperm with low hypo-osmotic swelling test scores with chymotrypsin on pregnancy rates after conventional in vitro fertilization-embryo transfer.

The embryos formed from fertilizing oocytes with sperm with subnormal hypo-osmotic swelling tests with conventional insemination rather than intracytoplasmic sperm injection are very unlikely to implant. The toxic factor transferred to the zona pellucida by such sperm can be negated by pretreating the sperm with the protein digestive enzyme chymotrypsin, resulting in markedly improved implantation rates.