1. male spermatozoa, weak sperm and deformed sperm (low sperm count, low viability and high malformation rate); 2. female cervical factors such as cervical scar, cervical tumour, cervical inflammation (difficult passage of sperm); 3. vaginal abnormalities leading to inability to have intercourse (vaginal scar, vaginal malformation, vaginal contracture due to psychological stress); 4. male factors leading to inability to deliver sperm into the female vagina (various factors leading to inability to have intercourse, hypospadias, excessive penile curvature, etc.); 5. immune infertility; 6. unexplained infertility (no obvious abnormalities found in both male and female partners during clinical examination, ineffective after simple clinical treatment).