A Self-Assessment Efficacy Tool for Spermicide Contraceptive Users

Easily accessible contraceptive methods, such as chemical and barrier methods, are currently used by about one in six U.S. women using contraception. Even in the face of suboptimal effectiveness, coitally dependent methods will likely always have a role in fertility management. As most contraceptive efficacy stratifications use population based data, in order for women to make informed decisions about the individual fit of a contraceptive method, better evidence-based, user-friendly tools are needed.

Spermicides are a readily-available, over-the counter, woman-controlled contraceptive method, but their effectiveness is user-dependent. Patient decision aids for spermicides and other barrier methods are not well developed and overall failure-rates could be improved by aids that account for individual characteristics. We sought to derive a prediction rule for successful use of spermicides for pregnancy prevention and to convert these data to a point-of-care instrument that women can use when considering spermicide use during contraceptive decision-making.

We pooled local data from three randomized clinical trials published in 2004, 2007, and 2010 that tested spermicide efficacy. We constructed a prediction rule for unintended pregnancy using bootstrap validation, and developed a scoring system.

Data from 621 women showed a mean age of 29 years; 49% were African-American and 43% Caucasian. The overall pregnancy rate was 10.3% over six months. In adjusted logistic regression, age >35 was protective against pregnancy and multi-gravidity was associated with high failure rates. These risk factors (together with frequency of unprotected sex) were used in a model that maximized sensitivity for pregnancy prediction to compute the predicted probability of unintended pregnancy for each woman. This model was 97% accurate in predicting women who had a <5% pregnancy risk while using spermicides.

Using prospectively collected data, we built a simple risk calculator for contraceptive failure that women can consult when considering spermicide use. This instrument could support patient-centered contraceptive decision-making.

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By: Schreiber CA1, Ratcliffe SJ2, Sammel MD2, Whittaker PG3.

• 1Penn Family Planning and Pregnancy Loss Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: schreibe@upenn.edu.
• 2Department of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
• 3Penn Family Planning and Pregnancy Loss Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. 

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