Contraceptive choice and missed pills

Contraception, Emergency Contraception & Pregnancy Termination

• Contraceptive eligibility: Use the current Australian clinical resource and the MEC framework it adopts, noting that WHO and UK classifications differ in detail. Core CHC contraindications include migraine with aura, severe hypertension and current breast cancer. Past disease, VTE on treatment and complicated diabetes need their specific category and circumstances rather than one universal label.

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Long-Acting Reversible Contraception (LARC)

Long-acting reversible contraceptives (LARCs) are the most effective methods of reversible fertility control because their clinical efficacy does not depend on daily compliance, coital timing, or frequent administration. Australian national guidelines strongly advocate for LARCs as first-line options for all individuals seeking contraception, including nulliparous women and adolescents.

Etonogestrel Subdermal Implant (Implanon NXT)

• Pharmacology & Duration: A single radiopaque rod ($4\text{ cm} \times 2\text{ mm}$) containing $68\text{ mg}$ of etonogestrel (the active metabolite of desogestrel). Licensed in Australia for 3 years of continuous use.
• Efficacy: The most effective reversible contraceptive available, with a failure rate of $< 0.05\%$ (higher efficacy than surgical sterilization).
• Mechanism of Action:
  1. Complete suppression of ovulation via inhibition of the mid-cycle luteinizing hormone (LH) surge.
  2. Rapid thickening of cervical mucus, preventing sperm ascent into the upper reproductive tract.
  3. Induction of an atrophic, hostile endometrial lining.
• Bleeding Patterns & Clinical Management: Unscheduled bleeding is the most common reason for premature discontinuation (~20% of users experience amenorrhoea, ~50% experience infrequent or light bleeding, and ~20% to 30% experience frequent or prolonged bleeding). Management of bothersome prolonged bleeding includes ruling out pregnancy and sexually transmitted infections (STIs), followed by a 3-month course of low-dose combined oral contraceptive pills (COCP) or a short course of oral mefenamic acid ($500\text{ mg}$ TDS) or tranexamic acid ($1\text{ g}$ TDS) taken during bleeding episodes.
• Fertility Return: Rapid return of fertility, with ovulatory cycles resuming within weeks of removal.

Levonorgestrel Intrauterine System (LNG-IUS)

• Available Devices in Australia:
  • Mirena: Licensed for eight years of contraception and five years for heavy menstrual bleeding. Duration for endometrial protection during menopausal hormone therapy is a separate indication; confirm current Australian product information and specialist guidance.
  • Kyleena ($19.5\text{ mg}$ LNG): Smaller frame and narrower insertion tube (suitable for nulliparous individuals with a small cervical canal). Licensed for 5 years for contraception.
• Mechanism of Action: Primarily a profound local progestogenic effect resulting in glandular endometrial atrophy and dense stromal decidualization, rendering the endometrium unreceptive to implantation. It also thickens cervical mucus. Most women continue to ovulate spontaneously because systemic progestogen absorption is minimal.
• Clinical Indications: Extremely effective contraception (failure rate $< 0.2\%$). Mirena is the recognized medical first-line therapy for heavy menstrual bleeding, reducing objective menstrual blood loss by $> 90\%$ within 6 months, and is highly effective in managing pain associated with adenomyosis and endometriosis.

Copper Intrauterine Device (Cu-IUD)

• Devices & Duration: TT380 Standard (licensed for 10 years) and TT380 Short (licensed for 5 years).
• Copper-IUD EC: Copper impairs sperm function and prevents fertilisation; it does not terminate an established pregnancy. Timing is assessed against intercourse and estimated ovulation, with pregnancy exclusion and infection considerations before insertion.
• Side Effects: Failure rate $< 0.8\%$. Users frequently experience heavier menses, prolonged menstrual flow, and increased dysmenorrhoea. It is contraindicated in unexplained abnormal uterine bleeding, active pelvic infection, severe uterine anatomical distortion, and Wilson disease.

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• Combined hormonal methods: Discuss locally available formulations, contraindications, bleeding preferences and adherence. Do not assume every product licensed overseas is available in Australia.

Mechanism of Action

• Oestrogen Component: Suppresses pituitary secretion of follicle-stimulating hormone (FSH), preventing dominant follicle selection and development.

• Progestogen Component: Suppresses the mid-cycle LH surge, preventing ovulation. It also thickens cervical mucus to impede sperm penetration and induces endometrial atrophy.

• MEC Category 1: A condition for which there is no restriction for the use of the contraceptive method.

• MEC Category 2: A condition where the advantages of using the method generally outweigh the theoretical or proven risks.

• MEC Category 3: A condition where the theoretical or proven risks usually outweigh the advantages. Method is not recommended unless other methods are unavailable or unacceptable.

• MEC Category 4: A condition that represents an unacceptable health risk (Absolute Contraindication).

Absolute Contraindications (MEC 4) for Combined Hormonal Contraceptives

1. Migraine with Aura at Any Age: Conveys an unacceptably high relative and absolute risk of ischaemic stroke due to the synergistic prothrombotic and vasoconstrictive effects of exogenous oestrogens.
2. Severe Hypertension: Systolic blood pressure $\ge 160\text{ mm Hg}$ or diastolic blood pressure $\ge 100\text{ mm Hg}$, or hypertension associated with end-organ vascular disease.
3. Smoking in Older Women: Age $\ge 35\text{ years}$ smoking $\ge 15\text{ cigarettes per day}$ (smoking $< 15$ cigarettes/day at age $\ge 35$ is MEC Category 3).
4. Venous Thromboembolism (VTE): Current or past personal history of deep vein thrombosis or pulmonary embolism; known inherited or acquired thrombogenic mutations (e.g., Factor V Leiden, Prothrombin gene mutation, Antithrombin III deficiency, Antiphospholipid syndrome).
5. Ischaemic Heart Disease & Cerebrovascular Disease: Known current or past history of coronary artery disease, stroke, or transient ischaemic attack.
6. Breast cancer: Current disease contraindicates hormonal contraception. Past disease requires its specific MEC category and oncology advice; it is not the same as current disease.
7. Complicated Diabetes Mellitus: Diabetes with established microvascular complications (nephropathy, retinopathy, neuropathy) or disease duration $> 20\text{ years}$.
8. Severe Hepatic Impairment: Decompensated cirrhosis, severe acute viral hepatitis, or benign/malignant liver tumours (hepatocellular adenoma or carcinoma).
9. Prolonged Immobilization: Major surgery with prolonged bed rest.
10. Early Postpartum: $< 6\text{ weeks}$ postpartum if breastfeeding (increases VTE risk and may suppress lactation).

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Missed combined pills

Use the Australian product/clinical flowchart for the pill concerned. For a conventional combined pill, more than 48 hours since the previous active pill means a pill has been missed. This differs from a US rule framed as two pills or 48 hours after the next pill was due. Take the most recent missed active pill, continue the pack and use condoms or abstain until seven active pills have been taken consecutively. If the lapse is near the start after a hormone-free interval, assess recent unprotected sex and emergency contraception. If fewer than seven active pills remain, omit the hormone-free interval and start the next active pack. Progestogen-only pills have formulation-specific lateness windows; do not apply combined-pill rules to them.

Emergency Contraception (EC)

Emergency contraception is indicated following unprotected sexual intercourse (UPSI) or potential contraceptive failure to prevent unintended pregnancy.

Primary references (checked 7 October 2026): Australian combined-pill flowchart; RANZCOG abortion guideline.