Associated factors of first-birth interval among women in reproductive age, addressing maternal and child health

Plain English summary Total Fertility Rate, which is the average number of live births that would be born to a woman over her reproductive life if she experiences the current age-specific fertility rates throughout her lifetime. The fertility pattern can be measured by several indicators such as the first-birth interval (FBI) after marriage. FBI is defined as the duration of time spent by married couples to have their first child since the first day of marriage. Some studies have demonstrated that the length of FBI subsequently influences spacing and childbearing pattern of a family. The aim of this study is first to determine the mean of FBI and second to explore the associated factors of FBI in Kerman, southern Iran. We analyzed data for 1350 women 15-49 years old. The outcome variable was the first-birth interval (FBI). Results showed that the average of FBI was 2.5 years. There is a positive association between FBI and age of wives at marriage, first menace age, wives' BMI, wives and husbands' educational level, contraception use, age of husbands at marriage, residence place, income sufficiency, and having engagement period. The women and men who got married at older ages were more likely to report short FBI. It was indicated that Educated women and men and women who experience menstruation at a younger age are more likely to report longer FBI. The knowledge about importance of FBI should be more announced for couples by health services in order to help them manage their child-spacing and fertility. The government also should pay attention on FBI as an important index in determining the average age of country population. Background The first-birth interval directly influences family size and maternal and child mortality. The objective of this study is to investigate factors associated with the time of the first-birth after the first marriage among women in Iran. Methods In this cross-sectional study, the first birth history of 1350 women aged 15-49 years was collected in Kerman (southern Iran) in 2018. To assess the predictor variables of the first-birth interval and calculate the adjusted hazard ratios, multivariate Cox regression was used. The P-value < 0.05 was considered as significant. The statistical analysis of data was performed using SPSS version 22. Results The average of the first-birth interval was 2.5 -/+ 0.8 years. Woman's age at marriage (HR 1.48, 95% CI 1.32-2.48), husband's age at marriage (HR 1.88, 95% CI 1.62-2.03), age at the first menstruation (HR 1.53, 95% CI 1.24-2.53), being rural residents (HR 2.041, 95% CI 1.26-2.95), and having engagement period (HR 1.85, 95% CI 1.52-3.05) were associated with short first-birth interval, and woman's BMI (HR 1.72, 95% CI 1.54-2.77), woman's university educational level (HR 1.47, 95% CI 1.35-2.57), husband' s university educational level (HR 1.39, 95% CI 1.32-2.51), contraception use (HR 2.28, 95% CI 1.12-2.86) and income sufficiency (HR 2.25, 95% CI 1.12-2.96) were associated with long first-birth interval. Conclusions Being a rural resident is the most influential predictor of short first-birth interval and income sufficiency is the most influential predictor of long first-birth interval.