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The Current Duration Approach to Estimating Time to Pregnancy


Niels Keiding, Department of Biostatistics, University of Copenhagen, P.O. Box 2099, DK-1014 Copenhagen K, Denmark.


Abstract.  Time-to-pregnancy (TTP) is the duration from the time a couple starts trying to become pregnant until they succeed. It is considered one of the most direct methods to measure natural fecundity in humans. Statistical tools for designing and analysing time to pregnancy studies belong to survival analysis, but several features require special attention. Prospective designs are difficult to carry out and retrospective (pregnancy-based) designs, being widely used in this area, do not allow efficiently including couples remaining childless. A third possible design starts from a cross-sectional sample of couples currently trying to become pregnant, using current duration (backward recurrence time) as basis for the estimation of TTP. Regression analysis is then most conveniently carried out in the accelerated failure time model. This paper surveys some practical and technical-statistical issues in implementing this approach in a large telephone-based survey, the Epidemiological Observatory of Fecundity in France (Obseff).