title: Contraceptive method at first sexual intercourse and subsequent pregnancy risk: findings from a secondary analysis of 16-year-old girls from the RIPPLE and SHARE studies.
abstract: OBJECTIVE
  Existing failure rate studies indicate that typical use of oral contraception (OC) results in fewer unplanned pregnancies than condom use, even among teenagers. However, comparative data on pregnancy risk associated with different contraceptive methods are lacking for younger teenagers starting their first sexual relationship. This study examined associations between contraceptive method at first intercourse and subsequent pregnancy in 16-year-old girls.
  
  
  METHODS
  Six thousand three hundred forty-eight female pupils from 51 secondary schools completed a questionnaire at mean age 16 years; 2,501 girls reported sexual intercourse. Logistic regression (N = 1952) was used to model the association of contraceptive method at first intercourse with pregnancy.
  
  
  RESULTS
  At first intercourse (median age 15 years) 54% reported using condoms only, 11% dual OC and condoms, 4% OC only, 4% emergency contraception, and 21% no effective method. Method used was associated with a similar method at a most recent intercourse. One in 10 girls reported a pregnancy. When compared to use of condoms only, greater pregnancy risk was found with no effective method (odds ratio [OR] 2.97, 95% confidence interval [CI] 2.12-4.15) or OC only (OR 2.44, 95% CI 1.29-4.60). Pregnancy risk for dual use and emergency contraception did not differ from that for condoms only. Both significant effects were partially attenuated by adjusting for user characteristics and sexual activity.
  
  
  CONCLUSIONS
  Young teenagers may use OC less efficiently than condoms for pregnancy prevention. The characteristics of those using OC-only confirm vulnerability to unintended pregnancy, and suggest that alternative contraceptive strategies should be considered for these young women.
authors.affiliation: Medical Research Council Social and Public Health Sciences Unit, University of Glasgow, Glasgow, United Kingdom. alison-p@sphsu.mrc.ac.uk
authors.forename: Alison
authors.initials: A
authors.lastname: Parkes
authors.forename: Daniel
authors.initials: D
authors.lastname: Wight
authors.forename: Marion
authors.initials: M
authors.lastname: Henderson
authors.forename: Judith
authors.initials: J
authors.lastname: Stephenson
authors.forename: Vicki
authors.initials: V
authors.lastname: Strange
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D003075:Coitus; D003267:Contraception / Q000379:methods*; D003268:Contraception Behavior; D003276:Contraceptives, Oral; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D016015:Logistic Models; D011247:Pregnancy; D011253:Pregnancy in Adolescence / Q000517:prevention & control*; D012307:Risk Factors; D012736:Sex Education / Q000379:methods; D006113:United Kingdom; D055815:Young Adult
chemical_list: D003276:Contraceptives, Oral