According to the 2002 National Survey of Family Growth (NSFG) approximately one-half of all pregnancies in the United States were unintended and almost one-half of these occurred in women using some form of reversible contraception. These rates have remained relatively unchanged since the previous survey reported in 1995. Addressing family planning and contraception is an important issue for providers of care to reproductive-age women. An increasing number of contraceptive options are becoming available on the US market. It is dependent on physicians and other health care providers to maintain currency with the recent advances in information concerning counseling, efficacy, safety, and side effects.
Finer LB, Henshaw SK: Disparities in rates of unintended pregnancy in the United States, 1994 and 2001. Perspect Sex Reprod Health 2006;38:90-96.
According to the 2002 NSFG, the combined oral contraceptive pill is the leading contraceptive method among women, with 19% of women between the ages of 15 and 44 choosing the pill. The introduction of lower-dose combination oral contraceptives (COCs) (<50 μg ethinyl estradiol) has provided many women a highly effective, safe, and tolerable method of contraception.
COCs suppress ovulation by diminishing the frequency of gonodotropin-releasing hormone pulses and halting the luteinizing hormone surge. They also alter the consistency of cervical mucous, affect the endometrial lining, and alter tubal transport. Most of the antiovulatory effects of COCs derive from the action of the progestin component. The estrogen doses are not sufficient to produce a consistent antiovulatory effect. The estrogenic component of COCs potentiates the action of the progestin and stabilizes the endometrium so that breakthrough bleeding is minimized. When administered correctly and consistently, they are greater than 99% effective at preventing pregnancy. However, failure rates are as high as 8%-10% during the first year of typical use. Noncompliance is the primary reason cited for the difference between these rates, frequently secondary to side effects such as abnormal bleeding and nausea.
The estrogenic agent most commonly used in COCs is ethinyl estradiol (EE), in doses ranging from 20 to 35 μg. Mestranol, which is infrequently used, is less potent than ethinyl estradiol such that a 50-μg dose of mestranol is equivalent to 30-35 μg of ethinyl estradiol. It appears that decreasing the dose of estrogen to 20 μg reduces the frequency of estrogen-related side effects, but increases the rate of breakthrough bleeding. In addition, there may be less margin for error with low-dose preparations such that missing pills may be more likely to result in breakthrough ovulation.
Multiple progestins are used in COC formulations. Biphasic and triphasic oral contraceptives, which vary the dose of progestin over a 28-day cycle, were developed to decrease the incidence of progestin-related side effects and breakthrough bleeding, although there is no convincing evidence that multiphasics indeed cause fewer adverse effects. The most commonly used progestins include norgestrel, levonorgestrel, and norethindrone. As with estrogens, some ...