Emergency contraception: how does it work?

Abstract Emergency (or post-coital) contraception is any substance or device that is used to prevent pregnancy after unprotected intercourse. Currently used hormonal methods of emergency contraception (high-dose combined oral contraceptive pill or levonorgestrel) prevent about 50–80% of pregnancies....

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Bibliographic Details
Published in:Reproductive biomedicine online 2009, Vol.18, p.32-36
Main Author: Baird, David T
Format: Article
Language:English
Subjects:
Contraception, Postcoital
Contraceptives, Oral, Combined - administration & dosage
Contraceptives, Oral, Combined - pharmacology
emergency contraception
Female
Humans
intrauterine device
levonorgestrel
Levonorgestrel - administration & dosage
Levonorgestrel - pharmacology
mifepristone
Obstetrics and Gynecology
Pregnancy
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Summary:Abstract Emergency (or post-coital) contraception is any substance or device that is used to prevent pregnancy after unprotected intercourse. Currently used hormonal methods of emergency contraception (high-dose combined oral contraceptive pill or levonorgestrel) prevent about 50–80% of pregnancies. Research has demonstrated that these methods inhibit the midcycle surge of LH from the pituitary and, if given at least 2 days before ovulation, ovulation is delayed or prevented. Ovulation still occurs if administration is delayed until ovulation is imminent. Biological data that suggest that the most likely mode of action is by preventing fertilization are supported by the clinical observation that the greater the interval between coitus and administration the greater the chance of pregnancy. There are no data supporting the view that levonorgestrel can impair the development of the embryo or prevent implantation. In contrast, other very effective methods of emergency contraception, such as mifepristone and intrauterine devices, can also inhibit implantation.
ISSN:1472-6483
1472-6491
DOI:10.1016/S1472-6483(10)60113-7