“Lowest-low fertility” has become widespread but is now less informative, Stuart Gietel-Basten and Ignacio Pardo argue. Countries sharing very low fertility levels increasingly follow divergent demographic trajectories. A single threshold no longer captures this diversity, calling for a less fertility-centered, more multidimensional perspective on population change.
The notion of “lowest-low fertility” emerged in the early 2000s to describe an unprecedented demographic development: total fertility rates (TFR) falling to 1.3 children per woman or below in a small group of European countries (Kohler et al. 2002). At the time, the concept provided a useful diagnostic tool, signaling a historically unique demographic trajectory, with potential implications for population ageing, labour force dynamics, and longer-term demographic sustainability.
Two decades later, the empirical landscape has changed substantially. Fertility levels below 1.3, no longer confined to a handful of countries, have spread across diverse regions, including East Asia, Southern and Eastern Europe, and parts of Latin America. As a result, a growing share of the world’s population now lives under what would be classified as “lowest-low fertility.”
At the same time, the analytical usefulness of the concept is further undermined by the widening range of fertility levels it now includes. Originally associated with a relatively narrow band below 1.3 children per woman, the category today spans TFRs from around 0.7 to 1.3. From a demographic perspective, this is a considerable range: differences within it translate into markedly distinct long-term population outcomes, particularly when compounded over time.
As the category has expanded geographically and substantively, its capacity to distinguish between demographic regimes has weakened. What was once a relatively coherent grouping now encompasses countries characterized by diverse demographic dynamics and varying levels of socioeconomic development and future prospects.
Diverging demographic trajectories
A limitation of the concept lies in its implicit assumption that similar fertility levels imply broadly comparable demographic futures. Increasingly, this assumption does not hold. Countries with TFRs below 1.3 display substantial variation in population trajectories, reflecting differences in migration, mortality, and age structure. For instance, while some countries with very low fertility face sustained population decline and rapid ageing, others continue to grow due to positive net migration. These differences are not marginal: they fundamentally shape the scale and pace of demographic change, as in the cases of Canada and South Korea, both “lowest-low” fertility populations.
Moreover, variation within fertility timing itself also matters (Sobotka 2017). In several Latin American contexts, recent declines are driven in part by the postponement of childbearing, particularly among younger cohorts, rather than by a uniform reduction in completed fertility. Such dynamics may imply different long-term outcomes than those observed in contexts where low fertility is more deeply entrenched across cohorts and the postponement transition is complete, providing less margin for recuperation.
At the same time, the persistence of the 1.3 threshold in public and policy discourse has contributed to a simplified narrative in which crossing a specific numerical boundary is equated with entering a zone of demographic crisis. This framing may inadvertently reinforce alarmist interpretations and direct attention toward policies aimed at increasing fertility, despite mixed evidence regarding their effectiveness.
Towards a multidimensional perspective
Reassessing the relevance of “lowest-low fertility” does not imply that fertility has become unimportant. Rather, it highlights the need to situate fertility within a broader analytical framework.
Population change reflects the interaction of multiple components—fertility, mortality, migration, and age structure—alongside the social and economic conditions that shape them. In many contexts, factors such as improvements in health, education, and productivity, or sustained migration inflows, may exert a stronger influence on demographic trajectories than modest variations in fertility. In fact, recent research further shows that, in some countries, changes in mortality can have a greater impact on population dynamics than shifts in fertility (Gietel-Basten et al. 2026).
A more comprehensive perspective would therefore move beyond single-threshold classifications and instead emphasize the diversity of demographic pathways observed across countries (Parr 2025). Such an approach is better suited to understanding contemporary population dynamics and to informing policy responses aligned with specific national contexts (Gietel-Basten & Pardo 2026).
References
Gietel-Basten, S., & Pardo, I. (2026). Beyond Lowest-Low Fertility: Why Post-Transitional Populations Follow Divergent Paths. Population and Development Review. https://doi.org/10.1111/padr.70052
Gietel-Basten, S., Pothisiri, W., & Scherbov, S. (2026). Investments in health and mortality reduction to address population decline. Bulletin of the World Health Organization, 104(2), 94–102. https://doi.org/10.2471/BLT.25.293627
Kohler, H.-P., Billari, F. C., & Ortega, J. A. (2002). The emergence of lowest-low fertility in Europe during the 1990s. Population and Development Review, 28(4), 641–680. https://doi.org/10.1111/j.1728-4457.2002.00641.x
Parr, N. (2025). Total fertility rates with immediate and very long run zero population growth implications for European countries. Genus Vol 81, article 27. https://doi.org/10.1186/s41118-025-00268-x
Sobotka, T. (2017). Post-transitional fertility: The role of childbearing postponement in fuelling very low fertility levels. Journal of Biosocial Science, 49(S1), S20–S45. https://doi.org/10.1017/S0021932017000323