There are strict definitions of infertility used by many doctors. However, there are also similar terms, e.g. subfertility for a more benign condition and fecundity for the natural improbability to conceive.

Reproductive endocrinologists, the doctors specializing in infertility, consider a couple to be infertile if:^[1]

• The couple has not conceived after 12 months of contraceptive-free intercourse if the female is under the age of 34
• The couple has not conceived after 6 months of contraceptive-free intercourse if the female is over the age of 35 (declining egg quality of females over the age of 35 account for the age-based discrepancy as when to seek medical intervention)
• The female is incapable of carrying a pregnancy to term.

• A couple that has tried unsuccessfully to have a child for a year or more is said to be subfertile.
• The couple’s fecundability rate is approximately 3-5%. Many of its causes are the same as those of infertility.
• Such causes could be endometriosis, or polycystic ovarian syndrome.