Infertility: assessment & investigation — NICE NG257 (2026), WHO 6th-edition semen criteria, and the structured couple workup

A 34-year-old teacher and her 36-year-old partner sit in your fertility clinic after 14 months of trying. Her cycles are regular at 28 days, his BMI is 29, neither smokes, and they are exhausted and anxious. Your job is not to fire off a battery of tests — it is to apply NICE NG257 (2026) cleanly: confirm the definition is met, assess BOTH partners in parallel, run the structured semen-hormone-reserve-tubal workup, reject the non-recommended tests, and know exactly when to step up to ovulation induction, IUI, or ART. The age on her chart is the single most important number in the room.[1][5]

Overview and definition

Infertility is common — roughly 1 in 6 couples globally (around 15 to 17%) and around 1 in 7 in the UK. The World Health Organization now defines it as a disease of the male or female reproductive system defined by the failure to achieve a pregnancy after 12 months or more of regular unprotected sexual intercourse. The NICE NG257 (2026) reframing is deliberately broader and inclusive: it covers anyone with a known clinical cause of infertility, OR who has not conceived after 12 months of regular unprotected intercourse, OR after 6 cycles of artificial insemination — and it applies regardless of sexual orientation, partnership status or gender identity.[1][4]

The clinical act that earns the mark is not the label but the timing of the assessment. A couple under 35 with no red flags gets lifestyle advice and a year of expectant management; a woman of 36 or older, or anyone with amenorrhoea, oligomenorrhoea, pelvic surgery, endometriosis, prior chemotherapy, or a known male factor, is investigated now.[1]