The appearance of sperm under a microscope is used to evaluate a man's fertility. All men, in a semen specimen, will have some sperm with a normal appearacne and some with an abnormal appearance. In men with normal fertility, a certain percentage of the sperm will have a normal appearance.

Over the years, different criteria have been used to distinguish normal from abnormal sperm and different "cutoff" levels have been used for what is considered "normal".

For many years, infertility specialists used criteria that were established by the World Health Organization (WHO). However, several recent studies found that the WHO criteria was not very good at distinguishing fertile men from infertile men.

For this reason, many of us have now switched to a different criteria known as the "Strict Morphology". It has also been referred to by the name of the doctor who developed it, Thinus Kruger, and is often called the Kruger morphology.

The concept behind strict morphology, as the name suggests, is to evaluate sperm much more closely than we had in the past and have a stricter determination for what is considered normal. For example, older criteria would consider a man normal if he had 30-50% normal sperm. A normal percentage under Kruger's criteria is 14% normal.

A normal morphology assessment using the Kruger method correlates much more closely with male fertility. Studies have even shown that the percentage of eggs that are fertilized during in vitro fertilization (IVF) correlate well with the percentage of normal sperm seen.

One problem that remained is that often the technicians performing the morphology would not evaluate semen samples consistently. There was often great variation from one day to the next or from technician to technician.