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  • Title: Post-ovulatory contraception.
    Author: Glasier A, Baird DT.
    Journal: Baillieres Clin Obstet Gynaecol; 1990 Jun; 4(2):283-91. PubMed ID: 2225600.
    Abstract:
    It is possible to prevent pregnancy after unprotected intercourse by suppressing ovulation, inhibiting fertilization or interfering with tubal transport and/or implantation of the early embryo. IUCDs probably prevent implantation by stimulating the release of prostaglandins from the endometrium but are not acceptable to many women. Post-coital contraceptive steroids, e.g. high-dose oestrogens, are associated with a relatively high incidence of side-effects and must be taken within 72 hours of coitus. As these agents are effective by creating a uterine environment unfavourable for implantation, it may be possible to use antigestagens or antioestrogens in this way. It is already known that an antigestagen in combination with a prostaglandin is a highly effective method of inducing abortion in very early pregnancy. The corpus luteum is essential for the maintenance of pregnancy and its destruction by a luteolytic agent should dislodge the implanting embryo. If an effective method of preventing implantation could be developed which was relatively free from side-effects, it should be possible to use it as a regular form of contraception to be taken only when the risk of pregnancy had occurred. The methods known to be practical for post-ovulatory contraception, defined as any substance or device used after coitus to prevent establishment of pregnancy up to 14 days after ovulation are reviewed. Most are used only in emergency for a single episode of unprotected intercourse or failed contraception, exceptions being the "visiting pill" of norethindrone used for migrant workers in China, and the IUD when inserted for this purpose as well as ongoing contraception. The physiology of ovulation, fertilization, transport of the ovum, and implantation of the blastocyst are reviewed. Estimates of the odds of becoming pregnant after an isolated unprotected intercourse range from 10-25%. High-dose estrogens, either stilbestrol (no longer used in the U.S.), ethinyl estradiol 5 mg, or conjugated estrogens 30 mg, have been used since early trials in the 1960s. Estrogen must be given for 5 days, started within 72 hours of coitus, and cause several unpleasant side effects, notably nausea, vomiting, mastalgia, and menstrual irregularity. Although no incidents have been reported, they are contraindicated for those at risk of thromboembolism. The failure rate is about 0.7%. Combined estrogen and progestagen, known as the Yuzpe method, consists of 2 dose of 100 mcg ethinyl estradiol and 1 mg norgestrel, repeated in 12 hours. The reported failure rates range from 0.2%-7.4%. Insertion of a copper IUD is effective post-coitally within 66 days, with failure rate less than 0.1%. The antiestrogen Danazol, which actually acts as an antigonadotrophin, can be used as a postcoital agent, in divided doses of 800 or 1200 mg 12 hours apart within 72 hours of exposure. Published failure rates are 2.5 and 0.9% with these doses. Progestagens alone have been studied by WHO, but failure rates were as high as 10.1% in women with frequent intercourse. Regular use was not recommended since cycles became unpredictable. Studies are being conducted on RU-486 and prostaglandins for postcoital use, in comparison with the Yuzpe regimen. A true luteolytic agent for women would seem to be the perfect postcoital agent, yet none exist.
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