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Purpose and principlesIndications, selection and cautionsAssessment before treatmentTreatment approachRegimens, contraindications and interactionsComplications, monitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Combined hormonal contraception eligibility and risks

Obstetrics and gynaecology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Act on thrombotic warning symptoms

Sudden breathlessness, pleuritic chest pain, haemoptysis, unilateral painful leg swelling, new focal neurology, severe unusual headache or visual loss may represent venous or arterial thrombosis.

Action: Stop further combined hormonal contraception pending urgent clinical assessment, direct the patient to emergency care, and ensure pregnancy prevention is revisited after the acute diagnosis.

Purpose and principles

Prescribe the combined pill, patch or vaginal ring safely by applying UKMEC, measuring blood pressure, explaining thrombosis risk and using clear starting and review rules.

CHC suppresses ovulation through negative hypothalamic-pituitary feedback, thickens cervical mucus and changes endometrium. Pill, patch and ring differ in route and use pattern but share oestrogen-related thrombotic concerns. Benefits include effective reversible contraception, predictable withdrawal bleeding, reduced menstrual loss and pain, and improvement in some acne. Explain that monthly withdrawal bleeding is not required for health and that extended or continuous use does not cause a harmful accumulation of blood.

Eligibility rests on a targeted history and objective blood pressure. Ask what migraine aura means rather than accepting an undifferentiated headache label: transient focal visual, sensory or speech symptoms preceding headache are important. Record smoking quantity and age, personal and first-degree family VTE history, thrombophilia, immobility or planned surgery, blood pressure, BMI, vascular disease, diabetes complications, breast and liver disease, postpartum and breastfeeding status. Use current UKMEC tables for combinations and changing conditions.

Indications, selection and cautions

Migraine aura phenotype

Fully reversible focal visual, sensory or speech symptoms are not the same as nonspecific blurred vision, photophobia or dizziness and materially alter CHC eligibility. Migraine with aura makes CHC UKMEC 4: do not use CHC and offer an appropriate alternative. Aura confined to at least five years ago is UKMEC 3 and requires the separate expert-assessment pathway.

Venous thrombosis phenotype

Unilateral swelling and pain, sudden breathlessness, pleuritic pain or haemoptysis requires urgent assessment while oestrogen exposure is withheld.

Arterial event phenotype

Sudden weakness, speech disturbance, visual loss or a severe unfamiliar headache can indicate stroke or retinal ischaemia and demands emergency care.

Extended-break risk

Missing active tablets beside the hormone-free interval creates the longest hormone-free time and the greatest chance that ovulation suppression will be lost.

Expected adaptation

Mild nausea, breast tenderness and irregular bleeding often improve over the first few cycles, provided pregnancy and serious pathology are not suspected.

Red flags requiring action

  • Current migraine with aura, previous venous thromboembolism, known thrombophilia, major vascular disease or severe hypertension can make oestrogen exposure an unacceptable risk.
  • A new severe headache, focal neurological symptom, chest symptom or unilateral leg swelling during CHC use requires urgent assessment rather than a routine contraceptive review.

Assessment before treatment

  1. 01
    Measured blood pressureFirst step
    Why
    Identify hypertension before oestrogen exposure and at clinically appropriate follow-up.
    Interpretation and limitations
    Confirm an unexpected reading correctly. CHC is UKMEC 4 at or above 160/100 mmHg; offer a safe alternative while hypertension is evaluated.
  2. 02
    Body mass index
    Why
    Contribute to vascular-risk and UKMEC assessment and inform route choice after relevant bariatric surgery.
    Interpretation and limitations
    BMI is one factor, not an isolated efficacy test. Consider its interaction with smoking, age, immobility and other thrombotic risks.
  3. 03
    Focused migraine history
    Why
    Distinguish aura from migraine without aura and non-migrainous headache before prescribing.
    Interpretation and limitations
    Migraine with aura is UKMEC 4 for CHC. A history of aura confined to at least five years ago is UKMEC 3: CHC is usually not recommended, and any exception requires expert clinical judgement when suitable alternatives are unavailable or unacceptable. New focal symptoms during use require cessation and urgent assessment.
  4. 04
    Pregnancy assessment
    Why
    Determine safe start timing and whether emergency contraception or later testing is required.
    Interpretation and limitations
    Use menstrual and sexual history with testing. If quick-starting after uncertain recent sex, retest 21 days after the last relevant exposure.

Treatment approach

01EligibilityFilter oestrogen risk before prescribingFirst stepA patient prefers a combined pill, patch or ring.+
  1. 1Measure blood pressure and BMI and take a focused history of aura, smoking, thrombosis, vascular disease, postpartum status, breast or liver disease, surgery and medicines.
  2. 2AlternativeApply current UKMEC, exclude category 4 methods and use expert judgement or a safer alternative for category 3 or important combined risk factors.
  3. 3Agree the formulation and route, explain absolute benefits and harms, and document the eligibility information supporting the decision.
02InitiationStart with precise backup adviceCHC is medically eligible and the patient wants to begin now.+
  1. 1Assess pregnancy risk and emergency-contraception need; a start on days 1–5 is immediately effective, while a later eligible start needs seven days of additional precautions.

Regimens, contraindications and interactions

A reasonable initial monophasic combined oral contraceptive for an eligible patient when no different hormonal profile or route is preferred.

Ethinylestradiol 30 micrograms with levonorgestrel 150 micrograms

Take one active tablet orally once daily for 21 days followed by a seven-day hormone-free interval, or use a supported extended or continuous tailored regimen with no break longer than seven days.

Do not use with UKMEC 4 conditions such as migraine with aura or severe hypertension; assess VTE, smoking, postpartum and medicine interactions and use product-specific missed-pill advice.

Complications, monitoring and follow-up

  • Recheck blood pressure after initiation according to clinical context and at least during ongoing contraceptive review; investigate sustained hypertension rather than repeatedly issuing CHC.
  • Ask about new migraine aura, severe headache, chest symptoms, unilateral leg swelling, smoking, surgery, immobility and vascular diagnoses at every safety review.
  • Review bleeding, nausea, breast symptoms, mood, sexual acceptability and adherence after an adequate trial, while excluding pregnancy or pathology when the pattern is concerning.
  • Reconcile prescribed and non-prescribed medicines, including enzyme inducers and St John’s wort, and provide bridging contraception before an interaction begins.
  • Confirm the exact regimen, hormone-free interval and missed-dose understanding rather than recording only that the patient takes a combined pill.

Special situations

Blood pressure is non-negotiable

Unlike pelvic examination or routine blood tests, a reliable blood-pressure measurement directly determines whether oestrogen can be prescribed safely.

Withdrawal bleeding is optional

It results from hormone withdrawal, not physiological cleansing; supported extended or continuous regimens can reduce bleeding and hormone-withdrawal symptoms.

The break drives failure

Extending the hormone-free interval is riskier than a single isolated active-tablet delay because ovarian suppression has longer to recover.

Route does not remove oestrogen risk

Patch and ring avoid daily tablets but remain combined hormonal methods and therefore share major UKMEC vascular contraindications.

New aura changes continuation

A patient eligible at initiation can become ineligible; new focal neurological symptoms require reassessment rather than automatic repeat prescribing.

Common pitfalls

  1. 01

    Prescribing CHC from a self-reported normal blood pressure without obtaining a reliable recent measurement.

  2. 02

    Confusing nonspecific headache symptoms with aura, or failing to ask about focal visual, sensory and speech phenomena.

  3. 03

    Assuming the patch or ring avoids thrombotic eligibility rules because the medicine is not swallowed.

  4. 04

    Insisting on a monthly withdrawal bleed or allowing a hormone-free interval longer than seven days.

  5. 05

    Ordering routine thrombophilia screening instead of taking an accurate personal and family thrombotic history.

  6. 06

    Stopping an unsafe method without arranging an effective alternative and accounting for recent intercourse.

Practice

Two practice questions

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Obstetrics and gynaecologyOriginal SBA

Pre-prescription safety measurement

A 24-year-old requests a combined pill and has no known medical condition. Which assessment is required before routine combined hormonal contraception is prescribed?

Choose one answer, then submit
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Sources and review status3 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

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.

  • CoSRH combined hormonal contraception guidelineEligibility, regimens, risks, interactions and follow-up.
  • CoSRH UKMEC 2025Current contraindication and risk-category tables.
  • NHS combined pillPatient-facing use, effectiveness, risks and access.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Do not start CHC when UKMEC category 4 applies. Current UKMEC identifies migraine with aura and severe hypertension of at least 160 systolic or 100 diastolic as unacceptable risk. Category 3 scenarios usually require a safer alternative or specialist judgement. Multiple cardiovascular factors may increase risk beyond any single entry. Conversely, routine thrombophilia testing is not useful in someone without a clinical indication, and family history should be interpreted by relationship, age and event context.

Venous thromboembolism risk is increased by CHC but remains small in absolute terms for most eligible users and is lower than during pregnancy and especially postpartum. Risk varies with progestogen and oestrogen dose. If there is no reason to select another preparation, a pill with at most 30 micrograms ethinylestradiol plus levonorgestrel or norethisterone is a pragmatic starter. Explain common early effects such as nausea, breast discomfort and unscheduled bleeding and distinguish these from urgent thrombosis symptoms.

Provide a usable regimen. A common monophasic levonorgestrel 150 microgram/ethinylestradiol 30 microgram pill is taken once daily. It may be used as 21 active pills followed by a seven-day hormone-free interval, or in an extended or continuous tailored regimen supported by guidance. Never lengthen the break beyond seven days. Patch and ring schedules differ, so issue the product’s written instructions. Vomiting, severe diarrhoea and missed pills can reduce oral reliability.

For a new start within cycle days 1–5, protection is immediate. If starting later and pregnancy can reasonably be excluded, start now and use condoms or abstain for seven days. If recent unprotected intercourse creates pregnancy risk, consider emergency contraception before quick starting; after ulipristal acetate, delay hormonal contraception for five days because progestogen can reduce its effect. Arrange pregnancy testing 21 days after the latest relevant intercourse when needed.

At review, check measured blood pressure, correct use, bleeding, adverse effects, adherence and any new migraine aura, smoking, medicine, surgery or diagnosis. Advise stopping CHC at least four weeks before planned major surgery or an expected period of limited mobility when clinically appropriate, with alternative contraception. A person who becomes ineligible should be helped to switch without an avoidable contraceptive gap. Fertility returns promptly after stopping.

Key points

  • Combined hormonal contraception includes the combined oral pill, transdermal patch and vaginal ring; all contain oestrogen plus progestogen and share major vascular eligibility considerations.
  • Measure blood pressure and record BMI before starting. A pelvic examination, cervical screening, thrombophilia screen and routine blood tests are not prerequisites for an otherwise uncomplicated prescription.
  • Ask specifically about migraine aura, smoking and age, VTE or thrombophilia, hypertension, cardiovascular disease, breast cancer, liver disease, postpartum state, surgery and interacting medicines.
  • UKMEC category 4 examples for CHC include migraine with aura and blood pressure at or above 160/100 mmHg; do not prescribe while arranging confirmation or safer alternatives.
  • A preparation containing no more than 30 micrograms ethinylestradiol with levonorgestrel or norethisterone is a reasonable initial oral option when no competing preference exists because VTE risk is comparatively lower.
  • Standard 21/7 use is not physiologically necessary. Tailored regimens may use fewer or no hormone-free intervals, but any break must not exceed seven days and product-specific instructions matter.
  • Starting on days 1–5 of a natural cycle gives immediate protection; at other times quick-start if pregnancy can reasonably be excluded and use condoms or abstain for seven days.
  • Review blood pressure, adherence, new migraine or vascular symptoms, smoking, medicines and patient acceptability; routine short prescriptions should not create avoidable access gaps.
  • Major surgery with anticipated prolonged immobility requires advance method planning because CHC compounds perioperative venous thromboembolism risk.
  • Pregnancy symptoms after missed pills, an extended hormone-free interval, vomiting, diarrhoea or an interacting medicine require prompt pregnancy-risk and emergency-contraception assessment.
    • 05
    Selective vascular or liver assessment
    Why
    Investigate a clinical concern rather than screening every CHC user with blood tests.
    Interpretation and limitations
    Routine thrombophilia, liver-function or lipid testing is not required without an indication; abnormal history or examination determines targeted work-up.
  • 2Prescribe the exact product and regimen, including tailored use if chosen, and explain missed-dose, vomiting and diarrhoea instructions in writing.
  • 3Arrange a pregnancy test 21 days after the latest relevant unprotected intercourse where uncertainty remains and set blood-pressure and acceptability review.
    • 03New riskSwitch without losing protectionMigraine aura, hypertension, thrombosis, interacting treatment or major surgery arises during use.+
    1. 1Assess urgent symptoms first and stop further CHC immediately when thrombosis or an arterial event is suspected.
    2. 2Reclassify eligibility using the new diagnosis or medicine and offer an unaffected progestogen-only or non-hormonal method where appropriate.
    3. 3Plan overlap, backup and emergency contraception from the actual dates of CHC use so the safety switch does not create a pregnancy-risk gap.