Original Research

Lifetime Patterns of Contraception and Their Relationship to Unintended Pregnancies

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BACKGROUND: For the past 30 years many effective methods of contraception have been available, yet unintended pregnancy rates still range from 30% to 50% in many populations. We examined patterns of women’s contraceptive use throughout their lives and relate them to unintended pregnancy.

METHODS: A total of 396 women aged 18 to 50 years chosen by convenience sampling from a family practice residency office were interviewed in a cross-sectional study about their history of using and changing contraception, and whether they believed they became pregnant while using a method of contraception. We analyzed the data for correlations and significance using chi-square and Student t tests.

RESULTS: Most women had used both condoms and oral contraceptive pills, and tried an average of 3.54 methods during a lifetime. Two patterns of women’s use of contraception emerged that describe 75% of the women. One third of the women— those who indicated a pattern of following their first method with a less effective method—are significantly more likely to have an unintended pregnancy while using contraception (odds ratio=1.4). The other group (50% of the entire sample) used increasingly effective methods and were less likely to have an unintended pregnancy.

CONCLUSIONS: Pregnancy is an inherent natural consequence of sexual intercourse, even when using very effective contraceptive methods. By asking a few questions about a woman’s history of contraceptive use, physicians may be able to determine those who are more likely to be at risk for an unintended pregnancy.

There are many highly effective contraceptive methods available. Some, including oral birth control pills (OCPs), injectable and implantable hormones, and sterilization of both sexes, have ideal effectiveness rates higher than 98% for preventing pregnancy.

However, contraception is not always used ideally. Unplanned or unintended pregnancies do occur. In 1988, US women aged 15 to 44 years reported that 35% of their full-term pregnancies in the preceding 5 years were unintended,1 in some populations 60% of pregnancies were reported as unintended,2 and one third of these ended in abortion.3 Sixty-five percent of adolescent pregnancies are also unintended.4 And more than 1 million pregnancies annually are reported to have occurred from misuse of OCPs.3

Pregnancies that occur while the woman is using contraception are considered unintended. These types of pregnancies have poorer outcomes when carried to term than other pregnancies, including an increased incidence of premature birth and intrauterine growth retardation.5 This is an area of concern for the women, their partners, and the health care providers who help these women with contraception concerns.

The way women use and experience contraception profoundly affects its effectiveness.2,6 OCPs have been available for more than 30 years, implantable contraceptives for approximately 8 years, and injectable contraceptives for 5 to 7 years. Today, there are women who have had greater than 95% effective hormonal contraception available all their childbearing years. The purpose of our study was to discover what patterns of contraceptive use women developed during their childbearing years and how these patterns were related to unintended pregnancies.


We obtained a convenience sampling of women who visited an urban/suburban family practice residency office that is run by an open-panel health maintenance organization (HMO), but accepts more than 60 different health plans (including Medicare, HMO Medicare, Medicaid, HMO Medicaid, and self-pay) and includes maternity care. The practice has more than 25,000 patient visits annually (60% women) who are residents of eastern Baltimore, Maryland, and Baltimore County. Women patients and women relatives or friends of patients who entered the waiting room and were aged 18 to 50 years were asked to participate in a face-to-face half-hour interview by a medical student. Two medical students talked with 396 women during June and July 1999. The interviews were recorded by identification number only.

After giving informed consent, the women spent approximately 30 minutes answering questions about marital status, education, socioeconomic status, drug and cigarette use, and first and subsequent contraceptive experiences. Each woman was given a list of 20 methods of contraception and 20 reasons for discontinuation to help her; both lists had an “other” category. She was asked what contraceptive she remembered she had used first, for how long, and when she had changed methods and why; these questions were repeated for every method used since. The questionnaire had been pretested for 2 years in 2 previous studies of more than 600 women. Only 5 women refused to participate in our survey, most often because of time constraints.

One author (J.A.R.) entered the data in Excel (Microsoft Corporation; Redmond, Wash) spreadsheets. The statisticians at the MedAtlantic Research Institute converted the spreadsheets with the Statistical Package for the Social Sciences (SPSS, Inc; Chicago, Ill). Variables were analyzed for correlation and significance by Student t and chi-square tests. The patterns of contraceptive use were analyzed, and demographic values were compared.


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