Premature ovarian insufficiency (POI) is one of the most distressing diagnoses in reproductive medicine and one of the most important to identify promptly — the average delay from symptom onset to diagnosis is 3–5 years in the UK. POI affects approximately 1 in 100 women under 40 and 1 in 1,000 under 30. The diagnosis requires: FSH >25 IU/L on two occasions 4 weeks apart + oligo/amenorrhoea for >4 months + age under 40. Beyond the immediate fertility implications, POI carries significant long-term health risks: osteoporosis (bone density falls rapidly without oestrogen), cardiovascular disease (loss of cardioprotective oestrogen effect), cognitive decline risk (some studies show increased dementia risk without HRT), and menopausal symptoms. HRT (not the combined oral contraceptive) is mandatory for all women with POI until the natural age of menopause (approximately 51) — the dose used is higher than standard menopause HRT to replace the level of oestrogen a woman of that age would naturally have. GPs who diagnose POI should start HRT at the same consultation and refer urgently to specialist reproductive endocrinology/gynaecology. The genetics workup is also important: approximately 10–15% of POI is caused by chromosomal abnormalities (Turner syndrome mosaicism — karyotype), and approximately 3–5% by FMR1 premutation (fragile X) — both have implications for family members.

The male factor infertility proportion is frequently underestimated in clinical practice — male factor contributes to approximately 40% of infertility cases (sole cause in 20%, contributing factor in 20%), yet semen analysis is often delayed or deprioritised in favour of female investigations. NICE NG156 (Fertility problems) explicitly states that both partners should be investigated simultaneously — waiting for female investigations to be completed before requesting semen analysis delays diagnosis by months. The practical message: at the first infertility consultation, blood tests for the woman (FSH, LH, oestradiol on day 2–5; AMH; mid-luteal progesterone; TSH; prolactin) AND semen analysis for the man should be requested simultaneously, with a target completion within 4 weeks. Varicocele as a correctable cause: a varicocele (dilated pampiniform venous plexus — visible or palpable above the left testis, or bilateral) causes elevated scrotal temperature that impairs spermatogenesis. Surgical repair (varicocelectomy) improves semen parameters in approximately 60–70% of men and results in spontaneous conception in 30–40% — making it the most commonly identifiable and correctable cause of male infertility. All men with semen analysis abnormalities should have a scrotal USS to exclude varicocele.

The female age threshold for expedited referral (6 months rather than 12 months for women over 36) is a NICE NG156 recommendation that reflects the dramatic age-related decline in ovarian reserve and oocyte quality — a woman aged 38 has approximately 50% lower IVF success rate per cycle than a woman aged 32. Delaying investigation by 12 months in a woman of 37 means she is 38 at the time of first specialist review, 39 at the start of IVF, and potentially 40–41 by the time of the first embryo transfer. This age-related attrition makes every month of unnecessary delay clinically significant. The GP should communicate this clearly: 'I know a year feels like a long time to wait, but because of your age I want to start investigating now rather than waiting 12 months — time is genuinely important for fertility treatment success.' Examination of the male partner is routinely omitted in primary care — GPs should examine both partners at the first infertility consultation. A varicocele (detectable by clinical examination in approximately 15% of men presenting with infertility, but often missed without specific examination technique) can be identified in 5 minutes and if confirmed on USS, can be referred for surgical repair that may restore fertility without IVF.

The progesterone timing principle is one of the most common laboratory errors in infertility investigation — the 'day 21 progesterone' rule applies only to women with a standard 28-day cycle (where ovulation occurs on approximately day 14, and the mid-luteal phase progesterone peak falls on day 21). In women with longer cycles (e.g., 35-day cycle — ovulation around day 21), the progesterone test should be done on day 28 (7 days before the expected period). The instruction should always be: 'Take the blood test 7 days before your expected next period, not on a fixed day 21.' A low progesterone in a long-cycle woman tested on day 21 simply represents pre-ovulatory levels, not anovulation, and leads to an incorrect diagnosis of anovulatory infertility. This error results in unnecessary investigation and treatment. Document: 'Progesterone requested for 7 days before expected period (approximately day [X] for this patient's cycle).' AMH testing is now the preferred test for ovarian reserve in the UK infertility pathway — it is synthesised by granulosa cells of antral follicles, reflects the primordial follicle pool, is stable throughout the menstrual cycle (can be taken on any cycle day), and predicts response to ovarian stimulation for IVF. Low AMH (<5 pmol/L) indicates poor ovarian reserve and urgency for specialist referral; very high AMH (>50 pmol/L) indicates PCOS phenotype and risk of ovarian hyperstimulation syndrome (OHSS) with IVF.

NHS IVF eligibility varies enormously by ICB in England — this is one of the most frustrating aspects of infertility care in the NHS. NICE NG156 recommends 3 IVF cycles for eligible couples, but many ICBs fund only 1 or 2 cycles, and some have additional criteria (no existing children — including previous relationships, BMI thresholds, smoking status, age cut-offs). GPs should: (1) know their local ICB criteria (check the ICB website or contact the local fertility unit); (2) document that the criteria were checked and communicated to the patient; (3) advise private IVF options if NHS funding is unavailable or restricted. The emotional impact of discovering NHS IVF is not funded in their area, or that they do not meet the criteria, is significant — patients need empathetic counselling, not just a printed leaflet. Referral to a fertility counsellor (available at all licensed fertility units) is important for couples navigating these decisions. Donor egg IVF (for POI or low ovarian reserve), donor sperm IVF (azoospermia), and surrogacy are options that should be mentioned in appropriate cases — specialist fertility counsellors at licensed HFEA clinics provide this information.

The letrozole vs clomifene debate for PCOS ovulation induction was largely settled by the Legro et al. NEJM 2014 trial (n=750 women with PCOS) — letrozole produced significantly higher ovulation rates (61.7% vs 48.3%), higher live birth rates (27.5% vs 19.1%), and lower multiple pregnancy rates (3.4% vs 7.4%) than clomifene. The mechanism advantage of letrozole over clomifene is that it does not have clomifene's anti-oestrogenic effect on the endometrium and cervical mucus (clomifene is a partial oestrogen receptor antagonist, so while it stimulates follicular development, it simultaneously reduces endometrial receptivity — a potential explanation for its lower live birth rate despite similar ovulation rates). Despite this evidence, letrozole remains off-label in the UK for infertility (licensed for breast cancer), which is why many centres still initiate with clomifene. However, NICE NG156 update 2023 now includes letrozole as a first-line alternative to clomifene for PCOS ovulation induction. GPs can initiate clomifene for PCOS ovulation induction in primary care with appropriate training and USS monitoring — letrozole initiation is typically specialist-initiated.

Antioxidant therapy for male infertility has a physiological rationale that GPs should know — reactive oxygen species (ROS) cause sperm DNA fragmentation, which impairs fertilisation and early embryo development. Oxidative stress is elevated in men with varicocele, infection, smoking, obesity, and idiopathic male infertility. A Cochrane review (Showell et al. 2020) found evidence suggesting that antioxidant supplements (particularly combined preparations) may improve sperm parameters and possibly live birth rates, though the quality of evidence is low-moderate. The evidence is strong enough to recommend OTC antioxidant supplementation (vitamin E, C, zinc, selenium, coenzyme Q10) to all men with abnormal semen analysis awaiting specialist review — the intervention is safe, inexpensive, and may improve the semen analysis at specialist assessment. Commercial fertility supplements (Impryl, Proxeed, Zita West Male Fertility) are examples of combined antioxidant preparations designed for this indication. GPs should also advise: avoid anabolic steroids and recreational drugs (direct testicular toxins), reduce alcohol to <14 units/week, stop smoking (oxidative stress), avoid tight underwear and prolonged heat exposure (laptops on lap, hot baths — scrotal temperature elevation impairs spermatogenesis).

The evidence base for folic acid supplementation in neural tube defect prevention is one of the most robust preventive interventions in medicine — the MRC Vitamin Study (1991) showed a 72% reduction in NTD recurrence with 4 mg folic acid daily in high-risk women. Population-level supplementation at 400 mcg OD is effective for women at standard risk. The 5 mg dose for high-risk groups (previous NTD, diabetes, obesity, antiepileptics) is a NICE recommendation. A critical quality improvement opportunity: GPs should ensure that any woman of reproductive age who is not on contraception (or who is planning pregnancy) is advised to start folic acid — this includes women at fertility consultations, women having smear tests, women attending for contraception removal, and women at any routine review. Currently, approximately 50% of pregnancies are unplanned, and many women do not start folic acid early enough because they do not know they are pregnant until after the neural tube closes (approximately 28 days post-conception). The recommendation for starting folic acid proactively in any woman who might become pregnant is a simple, inexpensive, high-impact public health intervention.

OHSS (ovarian hyperstimulation syndrome) is the most serious acute complication of fertility treatment — it occurs when ovarian stimulation with gonadotrophins causes excessive follicular recruitment, leading to massive fluid shifts into the third space (ascites, pleural and pericardial effusions). Severe OHSS presents with: marked abdominal distension, severe nausea/vomiting, dyspnoea (from ascites pushing up the diaphragm), and oliguria (reduced circulating volume causing prerenal acute kidney injury). The most dangerous complications are: renal failure, respiratory failure, and VTE (haemoconcentration from third-space fluid + immobility from abdominal pain creates high VTE risk). OHSS risk is highest in: PCOS patients (high antral follicle count + high AMH), young women, previous OHSS, and when HCG trigger is given. GPs must recognise OHSS in women recently undergoing IVF stimulation — it can develop 3–8 days after egg collection. Any woman who has had egg collection and presents with severe abdominal distension or dyspnoea within 2 weeks of the procedure → 999. The fertility clinic's out-of-hours number should be called simultaneously.