Authors: Schreiber, Courtney A.; Sammel, Mary; Hillier, Sharon L.; Barnhart, Kurt T.

Source: American Journal of Epidemiology, Volume 169, Number 4, 15 February 2009 , pp. 515-521(7)

Publisher: Oxford University Press

Abstract:

The prevalence of unplanned pregnancies contributes to the methodological challenges of human immunodeficiency virus (HIV) prevention trials. In this paper, the authors discuss the incidence of pregnancy, including chemical pregnancy, and how the different methods of pregnancy diagnosis could affect the statistical power and calculated outcomes of HIV prevention trials. Study sample size inflation factors are estimated to aid in the design of clinical trials.The authors used published data of women attempting pregnancy as well as data from HPTN 055 (<ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="www.HPTN.org/research_studies/hptn055.asp">www.HPTN.org/research_studies/hptn055.asp</ext-link>) to estimate the percentage of early study discontinuation that would be associated with 3 diagnostic methods for pregnancy in a hypothetical clinical trial. They classified chemical pregnancies as false-positive pregnancy tests and showed the sample size adjustment that would be necessary in clinical trial design because of the early discontinuations associated with pregnancy. There is a greater than 3-fold difference in the number of falsely positive pregnancy tests that will be detected, depending upon the diagnostic method used. The number of incident pregnancies may render HIV prevention trial sample sizes inadequate by as much as 50%. Pregnancy prevention and precise pregnancy diagnosis are critical to the statistical power and integrity of HIV prevention trials.

Keywords: clinical trials as topic; contraception; HIV; pregnancy; primary prevention

Document Type: Research article

DOI: http://dx.doi.org/10.1093/aje/kwn345

Publication date: 2009-02-15

More about this publication?

• The American Journal of Epidemiology is the premier epidemiological journal devoted to the publication of empirical research findings, methodological developments in the field of epidemiological research and opinion pieces. It is aimed at both fellow epidemiologists and those who use epidemiological data, including public health workers and clinicians.

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