title: Lifetime patterns of contraception and their relationship to unintended pregnancies.
abstract: 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.
authors.affiliation: Franklin Square Family Practice, Baltimore, Maryland 21237, USA. joannero@helix.org
authors.forename: J A
authors.initials: JA
authors.lastname: Rosenfield
authors.forename: K
authors.initials: K
authors.lastname: Everett
mesh_terms: D015142:Baltimore; D017280:Condoms; D003267:Contraception / Q000379:methods / Q000706:statistics & numerical data; D003273:Contraceptive Devices; D003276:Contraceptives, Oral; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008396:Maryland; D008525:Medroxyprogesterone; D011247:Pregnancy / Q000706:statistics & numerical data; D012307:Risk Factors
chemical_list: D003276:Contraceptives, Oral; D008525:Medroxyprogesterone