Nearly 90% of male infertility is due to low sperm count and poor sperm quality, the rest of the cases are related to anatomical issues, hormonal imbalance, and genetic defects.
According to WHO, sperm count less than 15million sperm/milliliter semen is considered as low sperm count or oligospermia. In few cases, men who can produce sperm cannot ejaculate sperm because of an underlying medical condition called azoospermia
In low sperm count, sperms cannot reach the vas (tube that transport sperm) because of the less quantity whereas, in poor sperm quality, sperm cannot swim towards the egg. Thus, low sperm count and poor sperm quality hinders fertilization.