Impaired delivery of sperm to the egg
Causes may include:
Blockage of epididymis or ejaculatory ducts: Obstructuions block the normal passage of sperms. They can be caused by a number of factors, such as repeated infections, prior surgery (including vasectomy), and inflammation or development problems. Any portion of the male reproductive tract, such as the vas deferens or epididymis, can be obstructed, preventing normal transport of sperm from the testicles to the urethra, where it leaves the body during ejaculation.
a. Blockage due to developmental defects:Some men are born with blockage of the epidydimis or ejaculatory ducts. Men with cystic fibrosis, or who are carriers of cystic fibrosis often have a missing or obstructed vas deferens.
b. Blockage by infection:Repeated bouts of sexually transmitted diseases (STDs), such as Chlamydia and Gonorrhea, can cause scarring and block sperm passage.
c. Blockage due to trauma:Injury to the male reproductive tract can cause blockage. The absence of ejaculate may occur in men with spinal cord injuries or diseases.