Factors Affecting the Interval Between Marriage and the Birth of the First Child 2018-2023: A Retrospective Cohort Study.

BACKGROUND AND AIM: The interval between first births directly affects family size and maternal and child mortality. The aim of this study was to investigate the factors associated with the timing of first birth after first marriage among women in Sanandaj city. METHODS: In this retrospective cohort study, data from 1200 women aged 15 to 49 years were collected in Sanandaj city (western Iran) in 21 March 2018-2023. Multistage random sampling method was used in this study. The study population was divided into three categories of urban, urban-rural, and rural health centers. Data on the study subjects were collected for the final study between October and December 2024. Multivariate Cox regression was used to evaluate predictors of birth interval to marriage and calculate adjusted hazard ratios. RESULTS: In a study of 1200 subjects, 720 number of censored (60%), the median interval between the birth of the first child after marriage was 3.4 years (3.2-3.5). The multivariate Cox regression analysis revealed that each additional year of age at marriage was associated with a 7% increase in the hazard of having a shorter interval to first birth (HR = 1.07, 95% CI: 1.04-1.09, p = 0.001). The multivariate analysis also showed that a 1-year increase in age at menarche was associated with a 14% higher hazard of a shorter marriage-to-first-birth interval (HR = 1.14, 95% CI: 1.05-1.24, p = 0.001). Furthermore, women exposed to government incentive policies had a 45% higher hazard of experiencing a shorter first birth interval (HR = 1.45, 95% CI: 1.17-1.79, p = 0.001). CONCLUSION: Increasing age, increasing age of menarche, and government incentive policies are the most effective predictors of a short interval between births after marriage. The government's attention to incentive policies and their support can lead to a decrease in the interval between births after marriage.