Delayed first births and completed fertility across the 1940–1969 birth cohorts

BACKGROUND The rise in the age at first birth has been universal in low-fertility countries in the last decades. Mothers who have their first child later tend to have fewer children, and in the absence of fertility catch-up at older ages, delayed fertility contributes to cohort fertility decline. OBJECTIVE We aim to study how changes in completed cohort fertility (quantum) relate to delayed age at first birth (tempo) across birth cohorts. METHODS We use birth histories collected in surveys or censuses in ten high-income countries. We rely on a decomposition analysis that quantifies how much the changes in age at first birth, mothers’ completed fertility conditional on age at first birth, and childlessness contribute to the total change in cohort fertility over the 1940–1969 birth cohorts.