Many people do not end their reproductive years with the family size they once imagined. This might be because their preference changed over time or because they ran into challenges that made it hard for them to achieve their goals. As people wait longer and longer to start their families, infertility is an obstacle that is likely to matter more and more in determining whether they have the number of children they want.
Yet, infertility often remains hidden within broader discussions of unmet fertility ideals and low fertility, rather than being measured directly. This leaves an important question unanswered: How much does infertility contribute to people falling short of their ideal family size? To answer this question, we use new cross-national data from the Generations and Gender Survey covering 10 low-fertility countries. In our Population and Development Review paper, “Infertility and Unrealized Family Size,” we examine how often people end up with fewer children than they would have ideally wanted and the extent to which infertility is part of that story.
How should we measure the mismatch between reproductive ideals and outcomes? Many studies ask young adults about their family plans and follow up years later. But a 22-year-old’s response to “How many children would you like to have?” often reflects a broad ideal rather than a concrete plan. By age 45, the same person may answer differently as their life circumstances and priorities evolve. We therefore took a different, retrospective approach. We analyzed responses from people nearing the end of their reproductive years (ages 42–50) who were asked about the number of children they would have ideally wanted, and we compared this stated ideal with their actual number of children. By doing so, we captured those whose parenting desires genuinely went unmet, filtering out the natural adjustment of preferences over time.
Our findings show that across countries between a quarter and a half of men and women end up having fewer children than they consider ideal. In most cases, not having children and having only one child are unwanted outcomes as around three-quarters of people in these categories express a preference for more children. Infertility plays a significant role in this gap. Individuals who report having experienced difficulties conceiving are far more likely to end up with fewer children than they wanted, even after accounting for partnership history and other life circumstances. Importantly, this pattern is visible not only among those who remained childless (the likelihood of this gap is about a quarter higher for women and about a fifth higher for men when infertility is reported), but also among parents who had children but fewer than they had hoped for. Both the high share of people with unrealized fertility ideals and the strong association between infertility and falling short of those ideals are remarkably consistent across countries, despite large differences in family norms, gender roles, and access to assisted reproductive technology.
Our results demonstrate that falling short of one’s ideal family size is not simply a matter of changing preferences or choosing a childfree life. For many people, it reflects constrained choices shaped by biological limits and the timing of family formation. This has important implications for how we understand low fertility and for how societies can support people in achieving the families they wish to have. A significant share of low fertility reflects unrealized ideals, which governments should explicitly recognize. Infertility, in this sense, is not a marginal issue: it is an important structural factor with considerable influence on demographic outcomes. This understanding should shift policy attention toward enabling earlier family formation, including more supportive social conditions that help people start families while they still have the biological capacity, and better public information about reproductive aging.
About the Authors
Ester Lazzari, University of Vienna
Eva Beaujouan, Wittgenstein Centre for Demography and Global Human Capital
Further reading:
UNFPA, U. N. P. F. (2025). State of World Population 2025: The Real Fertility Crisis – the Pursuit of Reproductive Agency in a Changing World (1st ed.). Bloomfield: United Nations Publications. https://www.unfpa.org/sites/default/files/pub-pdf/swp25-layout-en-v250609-web.pdf
Yeatman, S., & Smith-Greenaway, E. (2025). Unrealized fertility in demography. Demographic Research, 53, 1145–1172. https://doi.org/10.4054/DemRes.2025.53.36