Figure 10.1 Abortion rate*, ratio+, and percentage of total abortions by age group of women who obtained abortion, United States, 2006§. *Number of abortions per 1,000 women aged 15–44 years. +Number of abortions per 1,000 live births. §Data from 48 reporting areas, excludes California, Florida, Louisiana, and New Hampshire. (From Pazol K, Gamble SB, Parker WY, et al. Abortion surveillance—United States 2005. MMWR Surveil Sum 2009;58(SS08):35 [Figure 2].
From puberty until menopause, women are faced with concerns about childbearing or its avoidance: the only options are sexual abstinence, contraception, or pregnancy. The contraceptive choices made by couples in the United States in 2008 are shown in Table 10.1 (4). Oral contraceptives (OCs) were the first choice among women, used by 17.3%. Female sterilization was the second choice, used by 16.7%. With the addition of the 6.1% of couples relying on male sterilization, 22.8% of couples were relying on sterilization, making this the first choice of couples. Condoms were third choice, used by 10%. OC use declines with age, and the rate of sterilization increases. Twenty percent of women under 25 who use contraceptives use OCs and only 0.7% is sterilized. Of women aged 35 to 44 using contraception 17.3% uses OCs and 33.8% is sterilized, as is 13.9% of their consorts (Table 10.1). About 10% of women use more than one method of contraception. Although use of contraception is high, a significant proportion of sexually active couples (7.4%) does not use contraception, and each year, 2 of every 100 women aged 15 to 44 years have an induced abortion (4,5). Abortion is an obvious indicator of unplanned pregnancy. Abortion ratios by age group indicate that the use of abortion is greatest for the youngest women and least for women in their late 20s and early 30s who are most likely to continue pregnancies (Fig. 10.1). Use of abortion increases from the late 30s on. Young women are much more likely to experience unplanned pregnancy because they are more fertile than older women and because they are more likely to have intercourse without contraception. The effect of age on pregnancy rates with different contraceptive methods is shown in Figure 10.2.
Factors affecting whether pregnancy will occur include the fecundity of both partners, the timing of intercourse in relation to the time of ovulation, the method of contraception used, the intrinsic effectiveness of the contraceptive method, and the correct use of the method. It is impossible to assess the effectiveness of a contraceptive method in isolation from the other factors. The best way to assess effectiveness is long-term evaluation of a group of sexually active women using a particular method for a specified period to observe how frequently pregnancy occurs. A pregnancy rate per 100 women per year can be calculated using the Pearl formula (dividing the number of pregnancies by the total number of months contributed by all couples, and then multiplying the quotient by 1,200). With most methods, pregnancy rates decrease with time as the more fertile or less careful couples become pregnant and drop out of the calculations.
Figure 10.2 Percentage of women experiencing an accidental pregnancy, in the first 2 years of use, according to method, combined 1988 and 1995 National Survey of Family Growth. (From Ranjit N, Bankole A, Forrest JD, et al. Contraception failure in the first two years of use: differences across socioeconomic subgroups. Fam Plann Perspect 2001;33:25 [Table 6.]).