To begin with, it is important to know that the probability of conceiving during a normal, spontaneous cycle – without medical help – is only about 20% per cycle. 
About half of all couples wishing to have a child are successful within the first four months of "trying". In about three quarters of couples if "works" within a year. Societies for reproductive medicine advise that a fertility specialist be consulted if a woman does not conceive after 12 months at the latest. In couples over the age of 35, we would advise such a consultation after just six months.