Breakthrough bleeding on continuous combined HRT (ccHRT) in the first 3-6 months is expected and normal — this is the 'endometrial settling' period during which the combined oestrogen-progestogen suppresses the endometrium from its pre-HRT proliferative state. However, any bleeding beyond 6 months on ccHRT, or heavy/worsening bleeding at any time, is not normal and requires investigation. The critical principle: endometrial cancer can develop in women on HRT, and HRT use does not protect against endometrial cancer (combined HRT reduces but does not eliminate risk; oestrogen-only HRT significantly increases endometrial cancer risk — oestrogen-only HRT should never be prescribed to women with a uterus without concurrent progestogen). A GP who attributes prolonged or recurrent bleeding on ccHRT to 'the HRT' without performing a transvaginal USS and endometrial biopsy has missed the investigation that would identify endometrial cancer.

The distinction between sequential and continuous combined HRT is fundamental to interpreting bleeding patterns — sequential HRT is designed to produce a regular monthly withdrawal bleed (mimicking the menstrual cycle) by giving oestrogen continuously and progestogen cyclically for 12-14 days per month. The bleed occurs during or after the progestogen phase as the progestogen-primed endometrium sheds. This is expected and does not require investigation unless it is heavy, irregular, or occurs at unexpected times. Continuous combined HRT suppresses the endometrium completely — the woman should become amenorrhoeic within 3-6 months. The rationale for using ccHRT: women who are clearly postmenopausal (confirmed >12 months since last period) do not need or want a regular bleed. Using sequential HRT in a clearly postmenopausal woman unnecessarily maintains a monthly bleed. The NICE guideline on menopause (NG23) recommends: sequential HRT for women who are perimenopausal (still having some periods) or recently postmenopausal (within 12 months of LMP); continuous combined HRT for women who are clearly postmenopausal (>12 months since LMP).

The pipelle endometrial biopsy is the most important investigation for abnormal bleeding on HRT — it is a 3-5 minute outpatient procedure performed in community gynaecology or GP specialist clinics using a thin flexible plastic cannula (3mm diameter) inserted through the cervical os into the uterine cavity, which then samples the endometrium by aspiration. Sensitivity for endometrial cancer is approximately 90-95% (lower for focal lesions — hysteroscopy + directed biopsy is more sensitive for focal pathology). In UK practice, pipelle biopsy is the standard first-line investigation for abnormal bleeding before or alongside hysteroscopy. GPs with a special interest in gynaecology can be trained to perform pipelle biopsy in the practice (FSRH or RCOG-accredited training). For GPs without this skill, referral to community gynaecology or colposcopy clinic is appropriate. The NHS 2-week wait pathway for abnormal bleeding should be used where endometrial cancer cannot be excluded on clinical and USS grounds.

Micronised progesterone (Utrogestan) has an increasingly important role in HRT prescribing — multiple observational studies and the E3N cohort study suggest that Utrogestan (oral micronised progesterone, a bioidentical hormone identical to endogenous progesterone) has a significantly more favourable breast cancer risk profile than synthetic progestogens (medroxyprogesterone acetate, norethisterone, levonorgestrel) when used as the progestogen component of HRT. The MHRA 2020 guidance acknowledged this differential risk. Additionally, Utrogestan has better tolerability (fewer mood effects, less bloating, less androgenic side effects) and may have cardiovascular and sleep benefits through its progesterone receptor-mediated effects. The practical implication: for women who discontinue HRT due to progestogen intolerance, or who are concerned about breast cancer risk from combined HRT, switching from a synthetic progestogen to Utrogestan is a clinically appropriate and evidence-supported strategy. Utrogestan is taken orally (100 mg daily for ccHRT; 200 mg daily for 12-14 days/month for sequential HRT) and should be taken at night (its sedative side effect is then beneficial).

The 2-week wait referral for endometrial cancer is well-defined in NICE NG12 (Suspected Cancer) — the criteria relevant to HRT prescribers include: postmenopausal bleeding (any bleeding after 12 months of amenorrhoea in women not on HRT); unexpected vaginal bleeding in women on tamoxifen; and abnormal vaginal bleeding that does not fit the expected pattern in women on HRT, particularly after the initial settling period. GPs should be aware that NICE NG12 specifically recommends that women on HRT with bleeding that does not fit the expected pattern should be referred via the 2WW pathway rather than managed expectantly. The practical definition of 'expected pattern' is: regular withdrawal bleed on sequential HRT during/after the progestogen phase; amenorrhoea after 6 months on ccHRT. Any deviation from this expected pattern warrants investigation — and if investigation is unavailable promptly in primary care, 2WW referral is appropriate.

The Mirena LNG-IUS for endometrial protection with systemic oestrogen is an evidence-based and increasingly used combination — the levonorgestrel IUS provides highly effective local endometrial progestogen suppression with minimal systemic absorption. The NICE menopause guideline explicitly recommends the Mirena LNG-IUS as a licensed option for endometrial protection in women using any route of systemic oestrogen (oral, transdermal, gel, implant). The clinical advantages: (1) progestogen is delivered locally to the uterus — systemic progestogen side effects (mood, bloating, breast tenderness) are largely avoided; (2) the IUS lasts 5 years — eliminates daily medication compliance issues; (3) it also provides highly effective contraception (important for perimenopausal women who may still have ovarian activity); (4) it treats heavy menstrual bleeding concurrently; and (5) it is licensed for HRT endometrial protection (not off-label). GPs who fit coils should consider the Mirena LNG-IUS as a highly appropriate option for perimenopausal women wanting HRT who struggle with oral progestogen.

The management of atypical endometrial hyperplasia is a critical decision point — it represents the highest-risk premalignant endometrial lesion and approximately 30-40% of untreated cases progress to or coexist with endometrial cancer. NICE recommends hysterectomy as the definitive treatment for most women with atypical hyperplasia once family is complete. For women who wish to preserve fertility or who decline hysterectomy: high-dose progestogen therapy (Mirena LNG-IUS is the preferred option — direct endometrial delivery, highest regression rates) + 3-monthly endometrial biopsy surveillance. The regression rate with Mirena LNG-IUS for atypical hyperplasia is approximately 60-70% at 12 months. All HRT should be stopped or significantly revised (minimum required progestogen at absolute minimum dose) in women with atypical hyperplasia. After hysterectomy for atypical hyperplasia (with bilateral oophorectomy): oestrogen-only HRT can be started immediately — there is no contraindication (the uterus is removed, progestogen is no longer needed).

The cardiovascular timing hypothesis is one of the most important advances in understanding menopausal HRT in the last decade — the Women's Health Initiative (WHI) trial (2002) initially raised concerns about cardiovascular risk from HRT, but subsequent reanalysis showed that the adverse cardiovascular outcomes in WHI occurred predominantly in women who started HRT more than 10 years after menopause (average age 63 in WHI vs the typical HRT-starting age of 50-52). When HRT is started in the 'window of opportunity' — the first 10 years of menopause or before age 60 — observational studies and reanalysis of WHI data show a cardiovascular protective effect (approximately 30-50% reduction in coronary events). The mechanism: oestrogen has direct anti-atherogenic effects (anti-inflammatory, antioxidant, nitric oxide production, favourable lipid effects) but these effects are only operative in arteries that are not yet significantly atherosclerotic. This is why the NICE menopause guideline (NG23) explicitly supports starting HRT in symptomatic perimenopausal and early postmenopausal women without contraindications, noting the cardiovascular and cognitive benefits alongside bone and symptom benefits.

The annual HRT review is a NICE NG23 quality standard and a medicolegal requirement — GPs who prescribe HRT without annual review (particularly combined HRT) are exposed to medicolegal risk if a woman later develops breast cancer or endometrial cancer and the review would have identified the need for dose adjustment or investigation. The annual review should be documented explicitly in the clinical record with: indication (symptoms still present), formulation and dose, bleeding pattern (expected or investigated), BP, new contraindications checked, cervical smear status, breast screening status, benefits and risks discussed, patient's informed decision to continue. A brief consultation note stating 'HRT review — continue' without documenting the above does not meet the standard. Many GP practices use a structured HRT review template in their clinical system — this is best practice. The Menopause Specialist Society (BMS — British Menopause Society) provides GP HRT review templates and the e-learning HRT prescribing course which is recommended for all GPs prescribing HRT.