Unfortunately, it is not possible to predict when a wish to have a child will really come true. With some it happens the first time, others wait months to years. On average, it takes eight months for fertile couples with an active desire to have children to fall pregnant. However, average values do not say much more than just that. The decisive factors for conception are age, state of health and sexual behaviour. In general, couples should seek out medical advice after one year of unsuccessful trying. If you are older than 35, you should seek support after six months.

Check out another interesting article here.