There are two important factors to consider when judging a couple’s fertility: the age of the female partner AND the length of time a couple has been sexually active without using an effective form of contraception.
The monthly chance of pregnancy (called fecundity) depends on the age of the female partner, and decreases as a woman ages (read more below). For instance, a woman in her twenties has 25% fecundity, but as she approaches her 40s fecundity is less than 10%.
Furthermore, the chances of getting pregnant are highest during the first 3-6 months after discontinuing contraception (i.e. stopping the birth-control pill). After one unsuccessful year, irrespective of female age, remaining couples have a much smaller chance of pregnancy – without treatment, less than 3% per cycle (assuming the woman ovulates, sperm are present, and at least one fallopian tube is open).
The cause of infertility may be identified, but remains “unexplained” in approximately 20% of couples, meaning that a specific cause for their infertility is unknown. However, many successfully achieve pregnancy with treatment – often with simple interventions.