childbearing: the first birth interval and its determinants in the employees of tehran university of medical sciences, iran, 2018 - 2021

Background: childbearing is a major concern in some countries around the world. the fertility pattern can be described by several indicators, such as the first birth interval (fbi). objectives: this study aimed to predict the factors affecting the time of first birth. methods: this cross-sectional study is part of a cohort study in iran (2018-2021). the participants were 986 married women who were employees at the tehran university of medical sciences (tums) and enrolled by the census method. a checklist was used to collect information. data were described by mean, sd, frequency, and the effect of the variables on first birth and analyzed by the cox analysis. results: the adjusted hazard ratio (ahr) of the first birth was higher in the women with a high level of education than in those with a lower level of education (ahr = 0.29; 95% ci, 0.16 - 0.52; p < 0.001). also, the hazard of earlier first birth tripled in women with higher occupation levels than those with lower occupation levels (ahr = 0.34; 95% ci, 0.59 - 0.96; p < 0.05). the hazard of first birth was lower in married women under 20 years than in those with other cohort age groups (ahr = 1.87; 95% ci, 1.09 - 1.89; p < 0.001). conclusions: the age at first birth is significantly under the effect of women's education, occupation, marriage age, and wealth index.