The Contribution of Partnership Contexts of Births to Cohort Fertility Rates

Partnering behavior is central to understanding fertility. Influential concepts, including singlehood, serial monogamy, and multiple-partner fertility, are frequently used to analyze the interplay between partnering and fertility at the individual level. However, these frameworks are also evoked to understand population-level patterns. One fundamental population-level pattern for gauging the relationship between partnerships and childbearing, we argue, is the enumeration of fertility as the sum of births under various partnership conditions. Surprisingly, demographers rarely measure and do not yet have a clear picture of the extent to which childbearing in different partnership contexts contributes to completed fertility. We analyze Finnish register data to decompose the cohort fertility rate (CFR) into births from eight partner contexts, in conjunction with three dimensions: union status, union order, and reproductive partner order. Somewhat contrary to the discourse of partnering in the Nordics, births within first unions to first reproductive partners account for about two-thirds of CFR. Births in higher-order unions to first reproductive partners account for one-fifth. Single births and births with higher-order reproductive partners have a modest impact. This ranking holds across sex and educational level, with substantive relative differences. We argue that these descriptions provide an additional perspective to appraise childbearing and partnering dynamics.