The CHOICE protocol was approved by the Washington University in St. Louis School of Medicine Human Research Protection Office prior to initiation of participant recruitment. A more detailed description of the methods of CHOICE has been previously described [9
]. In the paragraphs below, we summarize the study design and analyses that are relevant to this specific research question.
The Contraceptive CHOICE Project, located in St. Louis, MO, is a prospective, observational study designed to remove financial barriers to effective contraception, promote the use of long-acting reversible methods of contraception (LARC) and evaluate use, satisfaction and continuation across both LARC and non-LARC methods in a cohort of 10,000 women. The LARC methods include the levonor-gestrel IUD, the copper IUD and the subdermal implant. The non-LARC methods include combined and progestin-only oral contraceptives, the transdermal contraceptive patch, the vaginal contraceptive ring, depot medroxyprogesterone acetate (DMPA) and barrier methods.
Enrollment began on August 1, 2007, and recruitment and follow-up are ongoing. Women interested in participating in CHOICE undergo an eligibility screen by trained staff. Inclusion criteria for CHOICE are as follows: age 14–45 years, residence in the St. Louis City or County or seeking services at designated recruitment sites, willingness to switch or initiate a new contraceptive method, sexual activity with a male partner or plans to become sexually active within 6 months and ability to consent in English or Spanish. Women who were surgically sterile, desired permanent sterilization or desired pregnancy within 1 year were excluded.
Enrollment is conducted in person by trained staff located at the recruitment location. Contraceptive counseling is provided to women prior to study enrollment in CHOICE. After hearing a standardized script regarding the effectiveness of LARC methods, participants are presented with evidence-based information about safety, effectiveness and risks and benefits of all reversible contraceptive methods. Counselors collect clinical information on each participant using a standardized form to identify conditions that may be a contraindication to a particular contraceptive method. Approval for the selected method is obtained from a clinician at the end of contraceptive counseling.
Following contraceptive counseling, study staff obtains written, informed consent for study participation. Assent is obtained for minors under 18 years, and the consent of one parent or legal guardian is obtained. Upon consent, the participant provides detailed contact information and self-collected specimens for sexually transmitted infection (STI) testing, and responds to a staff-administered structured baseline questionnaire. The questionnaire provides information about participant demographics, medical and reproductive history including sexual and obstetrical histories, and initial knowledge about the safety and effectiveness of available contraception methods. The participant receives her contraceptive method at the end of the enrollment session.
We performed a cross-sectional analysis of baseline data obtained during participant enrollment in the Contraceptive CHOICE Project (CHOICE). The data for this analysis were obtained from the baseline questionnaire of the first 5086 participants enrolled from August 1, 2007, through December 31, 2009. The inclusion criteria for our analysis were that the participants be 14–20 years of age. For the purpose of the analysis, they were categorized into two groups: 14–17- year-olds and 18–20-year-olds. Of the 5086 participants, 21% (n
=1,054) were aged 14–20 years [4% (n
=214) were aged 14–17 years and 17% (n
=840) were aged 18–20 years]. Frequencies, percents, means and standard deviations were used to describe demographic characteristics. Univariate analysis was performed using χ2
tests and, when appropriate, Fisher’s Exact Tests for categorical variables as well as Student’s t
test for continuous variables. Confounding was defined as either a greater than 10% relative change in the association between age and method choice with or without the covariate of interest in the model or prior evidence from the literature of a confounding effect. Confounders were included in the final multivariable model. Multivariable Poisson regression models with robust error variance were used to estimate relative risk (RR) and 95% confidence intervals (CIs) for the relationship between IUD and subdermal implant choice among the young women. This analytic approach provides an unbiased estimate of the RR when the outcome is common (>10%) [10
p Values and RRs and 95% CIs were used to describe statistical significance. All analyses were performed using SAS 9.2 (SAS Institute, Cary, NC, USA) and STATA 10 (StataCorp LP, College Station, TX, USA).
To test the hypothesis that the young adolescents would choose the subdermal implant over the IUD more frequently than the older adolescents, we divided participants aged 14–20 years who chose a LARC method into two groups: 14–17-year-olds and 18–20-year-olds. Assuming an IUD acceptance rate of 30% in young women and an odds ratio of 1.5 for subdermal implant acceptance (relative to IUD), a sample size of approximately 920 women aged 14–20 years provides >80% power to address the difference in LARC choice in younger women.