204989 Pregnancy Risk Index: Using behavioral data to predict pregnancy and infertility

Monday, November 9, 2009

John S. Santelli, MD , Department of Population and Family Health, Columbia University, New York, NY
Laura Lindberg, PhD , Guttmacher Institute, New York, NY
Mark Orr, PhD , Department of Population and Family Health, Mailman School of Public Health, Columbia University, New York, NY
Lawrence B. Finer, PhD , Research Division, Guttmacher Institute, New York, NY
Andrea J. Melnikas , Department of Population and Family Health, Columbia University, New York, NY

The Pregnancy Risk Index (PRI) is a simple mathematical method for calculating pregnancy risk using behavioral data.


To validate the PRI, we used data from women 15-44 years in the National Survey of Family Growth between 1982 and 2002. PRI scores are calculated based on a woman's sexual activity in the past 3 months, contraception use at last intercourse, and the relative efficacy of method(s) used - based on published contraceptive failure rates. We also reviewed published literature on contraceptive failure rates and infertility by age of woman.


Published contraceptive failure rates have changed little over 20 years in the U.S. We found that the PRI correlated well with actual pregnancy rates across demographic subgroups (R=.86). The PRI reproduced patterns of pregnancy by age, over time and among racial and ethnic subgroups. The PRI overestimated pregnancy risk among women 35-40 years (~2 fold), and women over 40 (~4 fold), even after adjustment for known infertility. Variation in coital frequency by age did not explain this finding. These data suggest considerable undiagnosed infertility beginning at age 35, approaching infertility estimates from natural fertility populations.


The Pregnancy Risk Index provides a readily calculated method to assess demographic trends and may be useful in evaluating intervention programs and simulating the impact of behavioral changes for women under 35. The PRI method may also be useful in estimating infertility from population data.

Learning Objectives:
Define the calculation of the Pregnancy Risk Index. Describe the potential utility of the Pregnancy Risk Index for public health. Identify issues in use of the Pregnancy Risk Indext in women 35-44 years.

Keywords: Contraception, Pregnancy

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am the principal investigator on this study, reviewed all data analyses, and wrote the abstract
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.