Background & Aim: Fertility is the most important factors affecting population fluctuations. Reproductive behaviors of a community can be studied through different methods. One of the methods is the evaluation of the interval between marriage and the birth of the first child. The aim of this study was to investigate the factors influencing the interval between marriage and first birth using the Cox regression model.

Methods & Materials: In this study, 1230 first-time mothers referred to urban and rural health centers of the city of Bandar Abbas were selected and studied in 2012-2013. The Cox regression model (proportional hazard) was performed to investigate the interval between marriage and first birth and the factors influencing this interval. Descriptive analysis of data was performed using SPSS software version 22 and data modeling was performed by R software version 3.2.1.

Results: In this study, the mean interval between marriage and first birth was 27.63 (±24.35) months. Based on the Cox model, mother’s age at marriage with HR(Hazard-Ratio)=1.13 (1.01–1.25) and place of residence with HR=1.28 (1.12–1.46) had significant effects on the interval between marriage and first birth.

Conclusion: The results of the current study compared to previous studies show that the interval between marriage and first birth has decreased, and some changes are observed in the factors influencing this interval.