Childbearing: The First Birth Interval and Its Determinants in the Employees of Tehran University of Medical Sciences, Iran, 2018 - 2021

 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).

 This study aimed to predict the factors affecting the time of first birth.

 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.

 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).

 The age at first birth is significantly under the effect of women's education, occupation, marriage age, and wealth index.