The decrease in ejaculate volume is called hypospermia and this happens when the volume of seminal fluid is below 1.5 ml. Among the most frequent causes of hypospermia is the age of the male, prostate surgery, inflammatory processes of the pelvis, and the male reproductive system.
Sometimes hypospermia is accompanied by a decrease in the concentration of sperm (oligozoospermia), which significantly reduces the chances of achieving a natural pregnancy and will require assisted reproduction treatments.