The enduring sub-replacement level of fertility in Iran is the result of changing timing of births. Using data from the 2015 Hamedan Survey of Fertility, conducted in a representative sample of 3000 married women aged 15-49, this study examined variations in median lengths of birth intervals employing cumulative survival functions, and investigated the determinants of birth interval lengths using regression hazard models. The results showed that the median first, second and third birth intervals, estimated at 28, 74 and 136 months respectively, doubled between 1995 and 2015. The multivariate analysis results indicated the strong impact of contraceptive use and higher education on lengthening birth intervals, with greater effects on the timing of second and third births. The relative risks of second and third births were higher among rural migrants, unemployed women and those with shorter periods of breast-feeding and the death of a preceding birth. Only timing of the third birth was influenced by son preference. The implications of the results for low fertility and maternal and child health in Iran are discussed. © 2017 Cambridge University Press.

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education unemployment proportional hazards model regression analysis Proportional Hazards Models Islam married woman developing country Developing Countries human middle aged death fertility Iran Breast Feeding Young Adult Humans migrant human tissue Adolescent male female Socioeconomic Factors risk factor Multivariate Analysis socioeconomics pregnancy child health major clinical study adult statistical model contraceptive behavior Contraception Behavior family planning son Birth Intervals Child