This review provides an update of previous estimates of first-year probabilities of contraceptive failure for all methods of contraception available in the United States. Estimates are provided of probabilities of failure during typical use (which includes both incorrect and inconsistent use) and during perfect use (correct and consistent use). The difference between these two probabilities reveals the consequences of imperfect use; it depends both on how unforgiving of imperfect use a method is and on how hard it is to use that method perfectly. These revisions reflect new research on contraceptive failure both during perfect use and during typical use.

This review provides an update of previous estimates of first-year probabilities of contraceptive failure for all methods of contraception available in the United States. Estimates are provided of probabilities of failure during typical use (which includes both incorrect and inconsistent use) and during perfect use (correct and consistent use). The difference between these two probabilities reveals the consequences of imperfect use; it depends both on how unforgiving of imperfect use a method is and on how hard it is to use that method perfectly. These revisions reflect new research on contraceptive failure both during perfect use and during typical use.

Measuring the effect of age on fertility is difficult because so many people use artificial methods to control fertility. Data from Western communities employing no artificial methods, such as the Hutterites of North America, show a gradual decline in fertility with age, which becomes steeper after 40 and approaches zero by 49.12 Increasing age of the man, reduced coital frequency,3 and increasing duration of marriage4 may all influence this decline, but data from a community where late marriage was common showed a similar pattern: 16% of women married between 30 and 34 remained childless, as did 31% of those marrying between 35 and 39 and 69% of those marrying over 40.3 These studies may not be relevant to women in contemporary society, where contraceptive practices allow early sexual activity with'the option of delaying pregnancy for up to 20 years. During this time pelvic infection may reduce the chances of a future planned pregnancy.56 Tubal disease is not, however, an important cause of infertility,78 and there is no evidence that the prolonged use of oral contraception is detrimental to fertility.9 Indeed, it may protect against certain disorders associated with rising age and nulliparity, such as uterine fibroids."0 Of more concern is the idea that fecundity is declining in both men and women because of adverse environmental factors.6' These would predominantly affect older women because of the prolonged exposure of their oocytes to such influences, but deteriorations in semen characteristics have also been reported. 12 The study by Johnson et al is reassuring because it does not show a rise in involuntary infertility with age, although no information is available about women who may deliberately defer child-bearing until after 35 (28 March, p 804). Any adverse effect of aging would increase the number of couples presenting with "unexplained" infertility, and analysis of conception rates among couples thus classified confirms that the prognosis is inversely related to the age of the women at presentation.913 There is no evidence, however, that couples with unexplained infertility are any older at presentation than those in other diagnostic groups,'4 and age did not significantly affect prognosis for couples in these other categories.'516 In such studies it is difficult to control for an effect of aging in the man. Semen collected from men of proved fertility undergoing routine analysis before vasectomy or for screening as potential donors in artificial insemination by (© BRITISH MEDICAL JOURNAL 1987. All reproduction rights reserved. donor programmes shows an age related decline in sperm motility and morphological characteristics.'7 One study controlled for male factors and coital frequency by looking at women with azoospermic husbands who were artificially inseminated': a cumulative conception rate of 73% after 12 months in women aged 30 and under fell to 63% in those between 31 and 35 and to 54% in those over 35. Though supporting a decline in fecundity with age, these figures do not allow for the incre...

Emergency post-coital contraceptives effectively reduce the risk of pregnancy, but their degree of efficacy remains uncertain. Measurement of efficacy depends on the pregnancy rate without treatment, which cannot be measured directly. We provide indirect estimates of such pregnancy rates, using data from a prospective study of 221 women who were attempting to conceive. We previously estimated the probability of pregnancy with an act of intercourse relative to ovulation. In this article, we extend these data to estimate the probability of pregnancy relative to intercourse on a given cycle day (counting from onset of previous menses). In assessing the efficacy of post-coital contraceptives, other approaches have not incorporated accurate information on the variability of ovulation. We find that the possibility of late ovulation produces a persistent risk of pregnancy even into the sixth week of the cycle. Post-coital contraceptives may be indicated even when intercourse has occurred late in the cycle.

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