How do people get pregnant? In short, man meets women, or sperm meets egg. This is a very simple way of explaining it, but it helps in explaining what we do in terms of investigations and treatment of cases of delayed pregnancy.
On average, 30 % of couples trying will get pregnant every month. So, if we follow 100 couples, after one month 30 are pregnant and 70 are not.
Doing the math, after 12 months of trying, 10 of the original couples are not yet pregnant. It is these 10 couples who may need help.
And when we define delayed pregnancy, we say trying for one year. Exceptions to that rule will include men and women who are known to have conditions that delay pregnancy, for example, irregular or very long periods, PCO, potency issues, etc.
Also, if the woman is older than 38 or so, we prefer not to wait for one more year of trying. While male fertility does not seem to be directly related to male age, female fertility drops after age 35 or so, and drops faster as time goes on. After about 42-43, the chances of pregnancy in women using their own eggs really drop to very low levels.