Chávez VJÁ, Quiñones HJ

Language: Spanish
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ABSTRACT

Background: in the context of epidemiology, where discussion is often held about the frequency of congenital defects, two questions have generated considerable debate. The first one is "Which frequency measurement is considered appropriate: incidence, prevalence or both?", and the second is "How should such frequency measurement be designed: by rate, proportion or ratio?"
Objectives: the purpose of the present communication is to determine which indicator -incidence or prevalence- is more feasible to estimate the frequency of congenital defects, as well as what criteria should such an indicator meet to be designated as rate, proportion or ratio.
Methods: a presentation is made of several criteria about the unreliability of one of the terms under discussion used to estimate the frequency of congenital defects. Determination is performed of the appropriate indicator for such estimations.
Results: the incidence formula is not sufficiently applicable in practice, due to the significance of the time of emergence of congenital defects for the population exposed to risk. Prevalence, on the other hand, is not susceptible to losses due to fetal death or unknown pregnancy, since it focuses on the number of cases in a population at a given moment. This makes it calculable at any stage or age, and appropriate to study the frequency of congenital defects. With respect to terminology, it was defined that frequency measurements are either proportions or ratios, depending on the data to be included in the formula in question. However, for the sake of uniformity, reports from international regulatory agencies use practical, commonly used measurements such as rates beyond the conceptual integrity of the indicator.
Conclusions: if no clear indication is made of a measurement approved by consensus, the frequency of congenital defects should be measured with the indicators prevalence proportion or prevalence ratio, depending on the case.