Stopping and switching contraceptive methods: findings from Contessa, a prospective longitudinal study of women of reproductive age in England.

BACKGROUND: Discontinuation of, and change in, use of contraceptive methods contributes to high unplanned pregnancy rates. The aims of the Contessa study were to estimate the prevalence of and reasons for discontinuation and change and to assess the implications for preventive intervention. METHODS: Prospective cohort study of 1091 potentially fertile women aged 18-49, carried out during 2008, using a sample drawn from the Health Survey for England 2006, a random probability survey of health. We carried out a baseline survey followed by three further waves, exploring patterns of contraceptive use, characteristics of women experiencing each, and reasons for discontinuation and change. FINDINGS: A percentage of 3.7 of women were at risk of unplanned pregnancy and discontinued and/or changed a contraceptive method in a year, compared with 4.7% who were at risk of unplanned pregnancy and used no method. Compared with continuous users, stoppers and switchers were younger, better educated and more likely to be single. Women discontinued or changed their contraceptive method for reasons of ease of use, reliability, side effects or concerns over health effects. Barely a quarter of such decisions were influenced by medical staff. INTERPRETATION: Effective strategies to aid contraceptive adherence have proved elusive but, if found, could reduce unplanned pregnancy rates appreciably. Understanding of the factors contributing to successful contraceptive practice is essential to prevention of unintended pregnancy.