If a couple is having trouble getting pregnant, the first test the doctor will likely ask for is a semen analysis. Both men and women can have problems. In half of the infertility cases the main issue is with the male fertility. And usually male infertility is often caused by low sperm production. And there is another reason for a semen analysis and that is to make sure a vasectomy that is a procedure to prevent pregnancy was successful. It is usually done after 8 to 16 weeks of the surgery to see if a person is still making any healthy sperm.