Sperm count. Light microscope used for counting sperm at an in vitro fertilisation (IVF) clinic. A sample of ejaculate is mounted on to a slide containing a grid and studied under the microscope. Each square of the grid contains a known volume of ejaculate. The number of sperm per square is counted and an average taken. From this it is possible to calculate the number of sperm per millimetre of ejaculate. A count of fewer than 20 million sperm per millimetre is considered low and may need treatment. The motility (movement) and shape of the sperm are also studied.