Men's ability to produce viable and healthy sperm can change considerably over days, weeks or years. This can be caused by several factors including aging, exposure to certain chemicals, infection and certain illnesses. Most often seminal parameters (the things we measure on a semen analysis) vary significantly without specific cause. There are also factors that can temporarily lower your sperm count, such as stress and thermal exposure. Thus, it is fairly common that your current semen analysis differs from one done a few years or even a few weeks back. Minor differences can also be accounted for due to varying techniques used in different laboratories. However having an analysis performed in one laboratory versus another, should not create a significant enough difference to affect the results of a normal vs. abnormal semen analysis. Male Fertility Specialists usually like to see at least 2 semen analysis to feel confident of the patient’s baseline status.