Scenarios of Delayed First Births and Associated Cohort Fertility Levels.

Fertility rates among individuals in their 20s have fallen sharply across Europe over the past 50 years. The implications of delayed first births for fertility levels in modern family regimes remain little understood. Using microsimulation models of childbearing and partnership for the 1970-1979 birth cohorts in Italy, Great Britain, Sweden, and Norway, we implement fictive scenarios that reduce the risk of having a first child before age 30 and examine fertility recovery mechanisms for aggregate fertility indicators (the proportion of women with at least one, two, three, or four children; cohort completed fertility rate). Exposure to a first birth increases systematically in the ages following the simulated reduction in first-birth risks, leading to a structural recovery in childbearing that varies across countries according to their fertility and partnership regimes. Full recovery requires an increase in late first-birth risks, with greater increases in countries where late family formation is uncommon and average family sizes are larger: in scenarios where early fertility declines substantially (a linear decline from 50% at age 15 to 0% at age 30), first-birth risks above age 30 would have to increase by 54% in Great Britain, 40% in Norway and Sweden, and 20% in Italy to keep completed fertility constant.