Definition
Infertility is defined as a failure to become pregnant over a 12-month period despite exposure to regular, unprotected intercourse (5). This clinical definition is based on anticipated time to pregnancy, measured in months, and represents a prognosis-based approach towards defining the biological potential of a couple (4).
It provides practical guidance on when to initiate investigations, that is, at a point in time when 80% of couples could be expected to conceive. However, it does not take into account the age of the female partner and variations in individual prognosis among couples. Crucially, it does not signify sterility (i.e. absolute inability to conceive), and a proportion of couples labelled infertile have the capacity to conceive without treatment.Some epidemiologists define infertility as a lack of conception after 2 years in women of reproductive age (15-49 years) who are at a risk of becoming pregnant (sexually active, not using contraception) (6). This is similar to the clinical definition apart from the longer duration which results in the exclusion of around 10% of couples who conceive between 12 and 24 months.
For demographic purposes, infertility is described as an inability to become pregnant with a live birth, within 5 years of exposure, based upon a consistent union status, lack of contraceptive use, non-lactation, and continuation of the desire for a child (7). This definition is useful for monitoring fertility trends across different populations and geographical regions but is unhelpful in a clinical context.
Although each of the definitions is relevant in its own context, the inconsistencies between them lead to varying prevalence rates of infertility, making it difficult to estimate the true extent of the problem. This has led to the call for the development of a valid tool for defining infertility based on prognostic factors (8).