In recent years, the study of birth intervals has been a main determinant of the levels of fertility in the populations, as it is associated with rates of fertility and population growth. Objective: The purpose of this study was to firstly apply survival analysis for modeling of first birth interval and secondly to explore its determinants. Materials and Methods: In a cross sectional study, the fertility history of 858 women was collected in rural areas of Shiraz (southern Iran) in 2008. We

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... the survival analysis such as cox regression and alternative parametric models to evaluate the prognostic factors of first birth interval. Results: Among the explanatory variables of interest, age at marriage, level of women's education, and menstrual status had highly significant effects on the duration of birth interval after marriage (p<0.01). Conclusion: It is concluded that the suitable parametric models would be a useful tool for fitting to first birth interval, the fact that has been less paid attention to in researches.