The current duration (backward recurrence time) approach to estimating time to pregnancy

Niels Keiding
Department of Biostatistics, University of Copenhagen
nike@sund.ku.dk

Time to pregnancy is the duration from a couple starts trying to become pregnant until they succeed and 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 the general area of 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 time to pregnancy/end of pregnancy attempt 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 practice in a large telephone-based survey, the Observatoire de la fertilité en France (OBSEFF).