Emergency Contraception

Introduction

Emergency contraception reduces the risk of pregnancy after unprotected sexual intercourse (UPSI) or contraceptive failure, such as a missed pill, condom breakage, or a barrier method used incorrectly. Three methods are available in the UK: the copper intrauterine device (IUD), ulipristal acetate, and levonorgestrel, and choosing between them depends on the time elapsed since intercourse, the estimated day of ovulation, body weight, drug interactions, and patient preference.¹

A recurring exam and clinical point is that all forms of emergency contraception act before implantation - by delaying or inhibiting ovulation, or in the case of the IUD, also by a direct toxic effect on sperm and ova - and none disrupts an established pregnancy. If a pregnancy test taken later is positive, emergency contraception has not caused a miscarriage; it has simply not worked.

Copper intrauterine device

The copper IUD is the most effective form of emergency contraception, with a failure rate below 1%, and works primarily by a direct toxic effect on sperm and ova, and by inhibiting implantation.² It can be fitted up to 5 days after a single episode of unprotected sex, or up to 5 days after the earliest estimated date of ovulation in a cycle with UPSI on more than one occasion - whichever gives the longer window - which makes it usable later than either oral method in many cycles.

It has the major additional advantage of providing ongoing, highly effective contraception if left in place, turning a single emergency consultation into a long-term solution. Access can be a limiting factor, since it requires a trained clinician and appropriate facilities, which is less widely available out of hours than oral emergency contraception.

Ulipristal acetate

Ulipristal acetate 30 mg, a single oral dose, is a selective progesterone receptor modulator that delays or inhibits ovulation, and is licensed for use up to 120 hours (5 days) after unprotected sex.³ It is more effective than levonorgestrel, particularly when taken closer to ovulation, because it can still delay ovulation even after the luteinising hormone surge has begun, a point in the cycle at which levonorgestrel is no longer effective.

Efficacy of ulipristal acetate is reduced in patients with a body mass index over 26 kg/m² or weight over 70 kg, though it remains an option (with counselling about reduced efficacy and consideration of the copper IUD instead where possible).

Levonorgestrel

Levonorgestrel 1.5 mg (doubled to 3 mg in those with a body mass index over 26 kg/m² or weight over 70 kg) is licensed for use up to 72 hours after unprotected sex, and works mainly by inhibiting or delaying ovulation - it is ineffective if taken after the luteinising hormone surge has already triggered ovulation.³ Effectiveness declines the longer the delay from intercourse, which is why it should be taken as soon as possible rather than waiting.

Unlike ulipristal acetate, hormonal contraception can be started or continued immediately (quick-started) after taking levonorgestrel, without a need to wait, which makes it more convenient to combine with starting ongoing contraception at the same visit.

Drug interactions

Enzyme-inducing drugs (for example, certain anticonvulsants, rifampicin, and St John's Wort) reduce the effectiveness of both oral emergency contraceptives by increasing their hepatic metabolism.³ In a patient taking an enzyme-inducing drug, the copper IUD is preferred as it is unaffected; if an oral method must be used, the levonorgestrel dose is doubled, though even this may not fully restore efficacy, and the IUD should be discussed as the more reliable alternative wherever access allows.

Assessment and counselling

History should establish the timing of all episodes of unprotected sex in the current cycle, cycle length and regularity (to estimate the fertile window and day of ovulation), current contraceptive use, body weight, relevant drug history, and any contraindications to each method. Emergency contraception does not require examination in most cases, other than for IUD insertion.

Every consultation for emergency contraception is also an opportunity to discuss and, where appropriate, start ongoing contraception, since a request for emergency contraception often signals a gap in the patient's regular method. A full STI risk assessment and screening should also be offered where the sexual history indicates a need.

Follow-up

Patients should be advised to take a pregnancy test if their next period is more than 7 days late, is significantly lighter than usual, or is accompanied by symptoms of pregnancy, since none of the emergency methods is 100% effective. Vomiting within 2-3 hours of taking an oral emergency contraceptive requires a repeat dose (or consideration of the IUD), since absorption cannot be assured.

Ongoing contraception should be arranged before the consultation ends wherever possible, since emergency contraception provides no protection against pregnancy from further acts of intercourse later in the same cycle.

Red flags

Prognosis

Used correctly and promptly, all three methods substantially reduce the risk of pregnancy following unprotected sex, with the copper IUD offering the highest and most weight-independent efficacy. None of the methods has been shown to have any lasting effect on future fertility, and normal ovulatory cycles resume promptly, which is an important reassurance to give patients concerned about future family planning.