Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Provide dose-proportionate endometrial protection during systemic oestrogen and investigate unscheduled bleeding using the April 2026 NICE position and May 2026 BMS risk, timing and ultrasound thresholds.
Systemic oestrogen stimulates endometrial proliferation. In a person with a uterus, progestogen converts proliferative endometrium and prevents the excess hyperplasia and cancer risk of unopposed therapy. Protection must be proportional to both oestrogen dose and exposure duration. Confirm the actual oestrogen preparation, pumps, sprays, patch strength or tablets used, because patients may inadvertently combine old and new prescriptions. Ask exactly how many progestogen capsules or tablets are taken, on which days, and whether a 52 mg levonorgestrel IUD is in situ and within its HRT-protection interval.
Sequential HRT gives a planned withdrawal bleed after cyclic progestogen. BMS recommends at least 12 days of micronised progesterone or 10 days of norethisterone or medroxyprogesterone acetate per 28-day cycle. Current licensed oral micronised progesterone is 200 mg at bedtime on days 15 to 26; an alternative licence regimen is 100 mg at bedtime on days 1 to 25. Continuous combined therapy uses daily progestogen and aims for amenorrhoea. The August 2026 BMS dose table pairs low or medium oestrogen with micronised progesterone 100 mg nightly continuously or 200 mg sequentially; high-dose oestrogen needs 200 mg continuously or 300 mg sequentially under specialist-informed practice.
Predictable bleeding after the progestogen phase of sequential HRT is planned, although a change in timing, heaviness or duration still merits review.
Light irregular bleeding within six months of starting or three months of changing systemic HRT is common when cancer risk and examination are reassuring.
First bleeding after more than six stable treatment months, or more than three months after a change, falls outside the expected adjustment window.
Heavy or prolonged bleeding, two minor risk factors, or any major risk factor accelerates imaging or suspected-cancer referral regardless of regimen.
Missed progestogen, too few days per cycle, an expired HRT-protection interval or high-dose oestrogen with standard opposition increases endometrial concern.
Take away from food because food increases bioavailability, warn about drowsiness or dizziness, check soya or peanut excipients by product, and increase protection for high-dose oestrogen under current BMS guidance.
Confirm the intended regimen and oestrogen dose, review mood and bleeding effects, and seek specialist dosing advice when high-dose oestrogen is used.
Explain that Mirena is licensed for only four years of HRT protection despite longer contraceptive licensing; exclude pregnancy, infection, cavity distortion and unexplained bleeding before insertion.
A Mirena may remain contraceptively effective after its licensed four-year HRT-protection interval, so the indication and date must be recorded explicitly.
Endometrial protection that was adequate at a low oestrogen dose may become insufficient after dose escalation even when adherence has not changed.
Current NICE advice uses six months after starting and three months after changing systemic HRT, replacing simplistic older rules centred only on three months.
The expected endometrium differs by regimen, so applying the continuous-combined 4 mm threshold to sequential HRT would create inappropriate escalation.
A numerical thickness reassures only when the entire endometrium is uniform and fully visualised; focal or obscured tissue still needs further assessment.
Continuing unopposed systemic oestrogen because the person reports no bleeding or because delivery is through a patch.
Using the eight-year contraceptive licence of Mirena as if it were also the duration of HRT endometrial protection.
Referring every light bleed in the first weeks of HRT straight to cancer services without assessing timing, risk, examination and adherence.
Conversely, repeatedly adjusting HRT after late-onset, heavy or high-risk bleeding instead of arranging urgent imaging or cancer-pathway assessment.
Interpreting a thin but poorly visualised or heterogeneous endometrium as equivalent to a fully visualised uniform low-risk scan.
Increasing oestrogen to control symptoms without increasing progestogen when the current BMS dose-proportion table requires it.
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A low-risk patient using continuous combined HRT has late-onset light bleeding. Urgent transvaginal ultrasound fully visualises a uniform endometrium measuring 6 mm. What is the appropriate interpretation?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
A 52 mg levonorgestrel IUD provides strong local endometrial opposition and often improves bleeding control. The BMS and contraception specialists support five years of use with systemic oestrogen. This is not the same as contraceptive duration: Mirena is licensed for eight years of contraception but only four years for HRT endometrial protection, making the fifth year an evidence-supported off-label practice. Record indication and insertion date; do not assume an IUD that remains contraceptively effective is still within its labelled HRT interval.
Unscheduled bleeding is any bleeding on a regimen expected to be bleed free, or bleeding outside the planned withdrawal episode on sequential therapy. NICE changed its advice in April 2026: explain that bleeding is common in the first six months after systemic HRT starts and in the first three months after a dose or preparation change, ask about it at the three-month review, and advise prompt clinical contact when it occurs beyond those windows. The evidence for cancer prediction in HRT users is limited, so NICE explicitly signposts the joint BMS guideline reviewed in May 2026.
Assessment begins with timing, pattern and risk. Record the last natural menstrual period, HRT start and change dates, expected withdrawal bleed, duration, frequency, flooding, clots, pain, postcoital bleeding and adherence. Baseline major endometrial-cancer factors are BMI at least 40 and Lynch or Cowden syndrome; BMS also classifies prolonged under-opposition as major, including oestrogen-only HRT with a uterus beyond six months, tricycling beyond twelve months, prolonged sequential HRT after five years when started from age 45, or inadequate monthly progestogen for twelve months or more. Baseline minor factors include BMI 30 to 39, diabetes and PCOS, with shorter or less severe periods of under-protection adding further minor risk. Examine abdomen and pelvis as indicated, inspect vulva and cervix, update cervical screening if due rather than using it diagnostically, and test for infection or pregnancy when relevant.
In a low-risk patient whose bleeding began within six months of starting or persists within three months of changing HRT, adjust progestogen or preparation for up to six months in total. Check missed capsules, incorrect patch sequence, malabsorption, drug interactions and whether the dose of progestogen matches oestrogen. A combined product can reduce administration errors; a 52 mg LNG-IUD offers the highest amenorrhoea rates among progestogen approaches. If bleeding remains after six months of adjustments, discuss urgent TVUS within six weeks or stopping HRT and reviewing at four weeks when the person wishes to avoid investigation.
Imaging urgency rises outside the settling window or with risk. Offer urgent TVUS within six weeks if first bleeding occurs more than six months after initiation or more than three months after a change. Offer it at any time for prolonged or heavy bleeding, or with two minor risk factors. One major or three minor risk factors requires urgent suspected-cancer referral without waiting for ultrasound adjustment. If the endometrium is uniform and fully visualised, thickness at or below 4 mm on continuous combined HRT or 7 mm on sequential HRT is reassuring enough for six months of HRT adjustments. Values above those thresholds require urgent biopsy and/or hysteroscopy through the cancer pathway.
A thin scan is not a permanent exemption. Escalate if bleeding becomes heavier or persists after the adjustment interval, or if the endometrium is not fully visualised, heterogeneous or focal. After a normal biopsy, adjust progestogen and provide three months of reassurance; after normal hysteroscopy and biopsy, the BMS permits six months. Continue to consider cervical, vulval, vaginal, urinary and gastrointestinal bleeding sources. Do not stop necessary oestrogen abruptly without discussing symptoms, but safety and cancer exclusion take priority over maintaining a particular regimen.