Contraception

Learning Objectives

  • Describe how oestrogen and progesterone affect the menstrual cycle, endometrium and cervical environment.

  • Describe how intra-uterine contraception works.

  • Outline advantages, disadvantages and contra-indications of all methods.

  • Describe the basic practical principles of how and when contraception is prescribed to optimise its success rates.

  • Describe how contraceptive efficacy is measured.

Effects of Oestrogen and Progesterone on the Menstrual Cycle, Endometrium, and Cervical Environment

  1. Menstrual Cycle:

    • Oestrogen and progesterone regulate the hypothalamic-pituitary-ovarian axis via negative feedback.

      • High levels suppress GnRH, LH, and FSH, preventing follicle growth and ovulation.

    • Oestrogen:

      • Proliferates the endometrium during the follicular phase.

      • Increases expression of oxytocin receptors and gap junctions during labor.

    • Progesterone:

      • Stabilizes and differentiates the endometrium during the luteal phase.

      • Relaxes uterine smooth muscle to maintain pregnancy (quiescent uterus).

  2. Endometrium:

    • Combined oestrogen and progesterone (e.g., contraceptive pills):

      • Thin the endometrial lining, reducing implantation likelihood.

    • Progesterone prevents the secretory changes needed for implantation.

  3. Cervical Environment:

    • Oestrogen:

      • Thins cervical mucus, making it receptive to sperm during ovulation.

    • Progesterone:

      • Thickens cervical mucus, creating a barrier to sperm entry.

      • Reduces ciliary motility in the uterine tubes, impairing gamete transport.

How Intra-Uterine Contraception (IUC) Works

  1. Types of IUC:

    • Copper IUCDs:

      • Copper ions act as spermicide, killing sperm.

      • Induce local inflammatory response and prostaglandin production, preventing implantation.

    • Hormonal IUS (e.g., Mirena):

      • Releases progesterone locally, thickening cervical mucus.

      • Thins the endometrial lining, reducing implantation potential.

  2. Mechanisms:

    • Prevent fertilization and implantation.

    • Induce local inflammation, creating a hostile uterine environment.

Advantages, Disadvantages, and Contraindications of Contraceptive Methods

Combined Oral Contraceptive Pills (COCP)

  • Advantages:

    • Reliable, reversible, and unrelated to coitus.

    • Non-contraceptive benefits: reduced risk of ovarian/endometrial cancer, improved menstrual symptoms (e.g., menorrhagia, dysmenorrhea).

  • Disadvantages:

    • Requires strict adherence (21 days on, 7 days off).

    • Risks: venous thromboembolism (VTE), hypertension, mood changes, gallstones.

  • Contraindications:

    • Smoking over age 35, history of VTE, uncontrolled hypertension, focal migraines.

Progestogen-Only Methods

  • Advantages:

    • Suitable for breastfeeding women.

    • No oestrogen-related risks (e.g., clotting, gallstones).

  • Disadvantages:

    • Irregular bleeding patterns.

    • Requires precise timing for older progestogen-only pills (POP).

  • Examples:

    • Nexplanon (implant): Effective for 3 years.

    • Depo-Provera (injection): Effective for 12 weeks but associated with delayed return to fertility.

Intra-Uterine Devices (IUD/IUS)

  • Advantages:

    • Long-acting, reversible, non-user dependent.

    • Effective immediately after insertion.

  • Disadvantages:

    • Requires insertion by trained professionals.

    • May cause heavier periods (copper IUCD) or irregular spotting (hormonal IUS).

  • Contraindications:

    • Active pelvic infection, distorted uterine cavity, unexplained vaginal bleeding.

Barrier Methods (Condoms, Diaphragms)

  • Advantages:

    • Protect against STIs.

    • Non-hormonal, widely available.

  • Disadvantages:

    • Higher failure rate due to user error.

    • Latex allergies (in some cases).

Emergency Contraception

  • Levonelle (levonorgestrel):

    • Progesterone-only, delays ovulation if taken within 72 hours.

  • EllaOne (ulipristal acetate):

    • Selective progesterone receptor modulator, effective up to 120 hours.

  • Copper IUCD:

    • Most effective, can be inserted up to 5 days post-ovulation.

Sterilization

  • Advantages:

    • Permanent solution, low failure rate (male sterilization more effective than female).

  • Disadvantages:

    • Irreversible in most cases.

    • Risk of ectopic pregnancy if failure occurs.

Principles for Contraceptive Prescription

  1. Individualization:

    • Tailor choice based on age, health status, reproductive goals, and coexisting conditions.

    • Consider adherence likelihood and potential drug interactions.

  2. Timing:

    • Initiate contraception based on the menstrual cycle to ensure no pre-existing pregnancy.

    • Emergency contraception should be administered as soon as possible after unprotected intercourse.

  3. Follow-Up:

    • Regular reviews for long-term methods to monitor for side effects or complications (e.g., infection with IUCD).

Contraceptive Efficacy Measurement

  1. Pearl Index:

    • Measures the number of pregnancies per 100 woman-years of use.

    • Typical Use (accounts for user error): Higher failure rates than perfect use.

    • Perfect Use (strict adherence): Reflects method reliability without human error.

  2. Effectiveness:

    • COCP: Typical use failure ~8/100 woman-years; perfect use ~<1/100.

    • IUCD/IUS: Failure rate <1/100 woman-years.

    • Condoms: Typical use failure ~15/100 woman-years; perfect use ~2/100.

Summary

By manipulating oestrogen and progesterone, contraceptive methods can suppress ovulation, alter cervical mucus, and affect endometrial receptivity to prevent pregnancy. Different methods vary in efficacy, user dependency, and side effects. Contraceptive efficacy is optimized through proper patient counseling, adherence, and regular follow-ups to ensure safety and effectiveness. Let me know if you'd like to explore any method in more depth!