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Vasectomy is a surgical form of male sterilization that involves severing and sealing the vasa deferentia, preventing sperm from mixing with semen during ejaculation. Because a vasectomy does not impact the testes' ability to produce testosterone, hormone levels, libido, and sexual function generally remain unchanged. While vasectomy is highly effective in preventing pregnancy, with a success rate near 99.85%, rare cases of recanalization (spontaneous reconnection) can occur. Although vasectomy...
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Emergency contraception: how does it work?

David T Baird1

  • 1Centre for Reproductive Biology, University of Edinburgh, Simpson Centre for Reproductive Health, Edinburgh, UK. dtbaird@ed.ac.uk

Reproductive Biomedicine Online
|March 14, 2009
PubMed
Summary
This summary is machine-generated.

Emergency contraception, including hormonal pills, prevents 50-80% of pregnancies by delaying or preventing ovulation. These methods work by preventing fertilization, not by affecting embryo development or implantation.

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Area of Science:

  • Reproductive Health
  • Endocrinology
  • Pharmacology

Background:

  • Emergency contraception (EC) is crucial for preventing pregnancy post-unprotected intercourse.
  • Current hormonal EC methods (e.g., high-dose combined oral contraceptive pills, levonorgestrel) are effective but have limitations.

Purpose of the Study:

  • To elucidate the mechanisms of action for hormonal emergency contraception.
  • To differentiate the effects of EC on fertilization versus implantation.

Main Methods:

  • Review of existing research on hormonal EC (combined oral contraceptive pills, levonorgestrel).
  • Analysis of biological data and clinical observations regarding EC timing and efficacy.
  • Comparison with other EC methods like mifepristone and intrauterine devices.

Main Results:

  • Hormonal EC methods inhibit the midcycle luteinizing hormone (LH) surge, delaying or preventing ovulation if administered at least 2 days prior.
  • Efficacy decreases if administered closer to ovulation; ovulation still occurs if given when imminent.
  • Evidence suggests hormonal EC primarily prevents fertilization, with no data supporting effects on embryo development or implantation.

Conclusions:

  • Hormonal emergency contraception's primary mechanism is preventing fertilization by inhibiting ovulation.
  • Levonorgestrel does not impair embryo development or prevent implantation.
  • Mifepristone and intrauterine devices represent alternative EC methods with potential to inhibit implantation.