Contraception
Contraception works by interrupting one of a small number of physiological steps required for pregnancy (ovulation, sperm transport, fertilisation or implantation), and matching a method's mechanism, efficacy and risk profile to the individual is what UKMEC eligibility criteria formalise.
In a nutshell
Every contraceptive method interrupts ovulation, sperm transport, fertilisation or implantation, and grouping methods by that mechanism predicts both their efficacy and their risk profile. Oestrogen-containing methods carry a thrombotic risk that progestogen-only methods avoid; long-acting methods remove user error, making them the most effective in typical use.
Classic presentation
A patient requesting contraceptive advice or emergency contraception, whose medical history (thrombosis, migraine with aura, smoking, breast cancer) is screened against UKMEC categories before a method is offered.
Key points
- Oestrogen is what confers the thrombotic and vascular risk of combined methods; progestogen-only methods avoid it, which is why they are default when oestrogen is contraindicated.
- UKMEC categories (1-4) formalise eligibility for each method against a patient's individual risk factors.
- Long-acting reversible methods have typical-use efficacy close to perfect-use efficacy because they remove reliance on daily or per-intercourse adherence.
- A copper intrauterine device is the most effective emergency contraception because it acts on fertilisation and implantation, working even after ovulation, unlike hormonal emergency contraception which chiefly delays ovulation.
- Hormonal and intrauterine methods do not protect against sexually transmitted infections, so barrier method counselling remains relevant regardless of the primary method chosen.
- Migraine with aura and a history of venous thromboembolism are classic contraindications to combined hormonal contraception.
First-line investigation
A structured history and UKMEC risk assessment (thrombosis, migraine with aura, smoking, BMI, blood pressure) to determine which methods are safe to offer.
First-line management
Discussion of long-acting reversible contraception as a highly effective first-line option, alongside patient-preferred alternatives, with a copper IUD or oral emergency contraception offered where indicated.
Exam traps
- Migraine with aura is a contraindication to combined hormonal contraception, not migraine without aura: the exam distinguishes the two.
- The progestogen-only pill and the intrauterine system are often mistakenly assumed to carry the same thrombotic risk as combined methods; they do not, because they lack oestrogen.
- The copper IUD remains the most effective emergency contraception even several days after unprotected intercourse, when hormonal options have lost efficacy.
Educational content pending clinical review. Not medical advice.