The Science

The Science

Contraceptive methods work by disrupting one or more stages of the reproductive process—ovulation, fertilization, or implantation. The underlying mechanisms vary based on the type of contraception used.

Hormonal contraception

Hormonal contraceptives manipulate the body’s natural reproductive hormones—estrogen and progesterone—to prevent pregnancy by:

1. Suppressing Ovulation: Estrogen and progestin in combined hormonal contraceptives (like pills, patches, and rings) suppress the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) from the pituitary gland. This prevents the LH surge needed for ovulation, so no egg is released.

2. Thickening Cervical Mucus: Progestin increases the viscosity of cervical mucus, making it difficult for sperm to swim through the cervix.

3. Thinning the Endometrial Lining: Hormonal methods render the uterine lining less receptive to implantation of a fertilized egg.

Barrier methods

1. Barrier methods physically block sperm from reaching the egg.

2. Barrier methods include spermicides that chemically kill or immobilize sperm. These methods prevent fertilization without altering natural hormones or cycles.

3. Intrauterine Devices (IUDs)

Copper IUD (Non-hormonal)

1. Releases copper ions, which are toxic to sperm. It impairs sperm motility and viability, preventing fertilization.

2. May also inhibit implantation due to endometrial inflammation.

Hormonal IUD (e.g., Mirena)

1. Releases levonorgestrel, a progestin that:

2. Inhibits sperm motility and function.

3. Thickens cervical mucus.

4. Thins the endometrial lining.

5. In some users, suppresses ovulation.

Natural methods

These methods rely on awareness of fertility patterns to avoid intercourse during fertile days, this includes -

1. Calendar method tracks ovulation based on cycle length.

2. Cervical mucus method monitors changes in discharge consistency.

3. Basal body temperature method detects ovulation-related temperature rise.

They work by avoiding intercourse during the estimated fertile window.

Permanent methods

These work by preventing transport of egg or sperm. These methods are permanent and highly effective.

Tubectomy (Female Sterilization): Involves cutting or blocking the fallopian tubes, so eggs cannot reach the uterus or meet sperm.

Vasectomy (Male Sterilization): Involves cutting or sealing the vas deferens, blocking sperm from mixing with semen.

References

1. Trussell J. Contraceptive failure in the United States. Contraception. 2004 Aug 1;70(2):89-96.