The sample should never be obtained through coitus interruptus for several reasons:

Some part of ejaculation could be lost. Bacterial contamination could happen. The acid vaginal pH could be deleterious for sperm motility.Also is very important to label the sample correctly the recipient with patient identification, date, hour, abstinence days, among other data required to be known. The volume of the semen sample (must be more than 1.5 ml), approximate number of total sperm cells, sperm motility/forward progression, and % of sperm with normal morphology are measured. It is possible to have hyperspermia (high volume more than 6 ml) or Hypospermia (low volume less than 0.5 ml). This is the most common type of fertility testing. Semen deficiencies are often labeled as follows:

Oligospermia or oligozoospermia – decreased number of spermatozoa in semen
Aspermia – complete lack of semen
Hypospermia – reduced seminal volume
Azoospermia – absence of sperm cells in semen
Teratospermia – increase in sperm with abnormal morphology
Asthenozoospermia – reduced sperm motility
Necrozoospermia – all sperm in the ejaculate are dead
Leucospermia – a high level of white blood cells in semen
Normozoospermia or normospermia – It is a result of semen analysis that shows normal values of all ejaculate parameters by WHO but still there are chances of being infertile. This is also called as unexplained InfertilityThere are various combinations of these as well, e.g. Teratoasthenozoospermia, which is reduced sperm morphology and motility. Low sperm counts are often associated with decreased sperm motility and increased abnormal morphology, thus the terms "oligoasthenoteratozoospermia" or "oligospermia" can be used as a catch-all.
Zinc replaced by cadmium in DNA polymerase can be particularly damaging to the testes. DNA damage
Common inherited variants in genes that encode enzymes employed in DNA mismatch repair are associated with increased risk of sperm DNA damage and male infertility. As men age there is a consistent decline in semen quality, and this decline appears to be due to DNA damage. The damage manifests by DNA fragmentation and by the increased susceptibility to denaturation upon exposure to heat or acid, the features characteristic of apoptosis of somatic cells. These findings suggest that DNA damage is an important factor in male infertility. Epigenetic
An increasing amount of recent evidence has been recorded documenting abnormal sperm DNA methylation in association with abnormal semen parameters and male infertility. Until recently, scientists have thought that epigenetic markers only affect the individual and are not passed down due to not changing the DNA. New studies suggest that environmental factors that changed an individuals epigenetic markers can be seen in their grandchildren, one such study demonstrating this through rats and fertility disruptors. Another study bred rats exposed to an endocrine disruptor, observing effects up to generation F5 including decreased sperm motility and decreased sperm count. These studies suggest that environmental factors that influence fertility can be felt for generations even without changing the DNA.