How I understand it is that your sperm is always active. But due to testicular atrophy caused by A.S. (taken with out an anti-estrogen) the amount generated by the testes can very. Depending on the amount of A.S. you are taking, the type of A.S., and the amount of time you have been on your cycle. I hear stories of people gettin they're sugnificant other pregnant while on A.S. but I also have friends that will never bear childen due to extended amounts of testicular atrophy while taking gear. I personally am going to be on a cycle from the last week in August all the way through May. I will be switching from different anabolic compounds aproximately every four weeks.