The study arrives at a moment of sustained demographic interest in why birth rates keep falling in high-income countries. After hovering around 2.0 children per woman through the 1990s and early 2000s, the U.S. total fertility rate peaked at 2.12 in 2007, then declined steadily in the wake of the Great Recession to reach 1.62 in 2023. Similar patterns of delayed and reduced childbearing have been documented across Europe and East Asia, making the United States part of a broad international trend rather than an outlier. Earlier work suggests that this decline cannot be explained simply by women wanting fewer children overall. Instead, researchers have pointed to postponement of childbearing and a shrinking likelihood of achieving the fertility goals people form early in life — a dynamic that matters biologically because the prospects for conception and healthy pregnancy decline with age. The new paper asks whether a third ingredient — uncertainty — helps complete the picture.

The authors draw a conceptual distinction between three dimensions of uncertainty in fertility goals. The first, "goal uncertainty," refers to difficulty forming a goal at all — the classic "don't know" response to questions about whether one intends to have children. The second, "realization uncertainty," concerns whether people who do report positive intentions believe those intentions will actually be achieved. The third, "intensity of goals," is not strictly uncertainty but a related attitude: how strongly a stated intention is held, measured here by whether a woman would be bothered if she ended up childless. The authors argue that these dimensions, though analytically separable, may travel together and jointly shape fertility behavior. A woman who doubts she can afford a child, for example, may simultaneously report an intention, express low confidence in achieving it, and care less about the outcome — a bundle of attitudes that standard projections, which typically count only the intention itself, cannot distinguish.

To measure these dimensions, the team used the National Survey of Family Growth (NSFG), a nationally representative repeated cross-sectional survey that has tracked fertility attitudes and behaviors in the United States since 1973 and is administered by the National Center for Health Statistics. The analysis pooled data releases from 2002 through 2018, yielding a weighted sample of 41,492 women aged 15 to 44, with representative estimates for 2002, 2008, 2012, 2014, 2016, and 2018. Because each survey round draws a fresh sample rather than following the same people, the design captures period trends across the population rather than individual change over time. The NSFG asks respondents stepwise questions: first whether they desire another child, then whether they intend one, then — for those who intend — how sure they are they will actually have a baby, with answers ranging from "very sure" to "not at all sure." Childless women were also asked whether it would bother them a great deal, some, a little, or not at all if they had no children. Because the survey's male questionnaire does not ask unpartnered men about intention certainty, the analysis was restricted to women.

The first headline result concerns goal uncertainty, which turned out to be rare. Only between roughly 1.5 and 2.1 percent of women answered "don't know" when asked whether they intended more children, and that proportion was stable across the study period. Notably, the NSFG does not offer "don't know" or softer categories like "probably yes" as pre-coded options, so respondents must volunteer hesitation on their own; this figure likely represents a lower bound on true goal uncertainty. The proportion of women who did not provide uncertainty answers varied little by age, parental status, partnership status, education, or income, even as the underlying proportions of "yes" and "no" intenders differed sharply across these groups. In other words, American women overwhelmingly manage to form an opinion about whether they want more children — the interesting variation lies in what happens after that opinion is formed.

Realization uncertainty, by contrast, was pervasive. Among women who intended at least one more child, up to 50 percent were not "very sure" they would follow through, including about 7 percent who said they were "not at all sure." The aggregate level was broadly stable over time, but subgroup patterns diverged in revealing ways. Childless women were more certain of realizing their intentions than mothers — about two-thirds versus one-half reporting they were very sure — but their certainty declined over the period, from 60 percent in 2002 to 52 percent in 2018, while mothers' certainty rose from 46 to 50 percent. The authors suggest this closing gap may reflect a growing sense among young, childless women that the conventional path to parenthood has become harder to complete. Younger women were more certain than women aged 30 to 44, of whom more than half expressed uncertainty and up to 17 percent reported being not at all sure in 2008. Partnered women were slightly more certain than unpartnered women, consistent with the practical advantages a stable partner provides for pursuing parenthood.

Socioeconomic status also mattered. Women with at least a bachelor's degree and those with household incomes at or above 200 percent of the poverty line reported higher certainty about realizing their intentions. Yet even this advantage appeared to be eroding: among college-educated women intending more children, the share who were "very sure" fell from 65 percent in 2014 to 54 percent in 2018, while the share "not at all sure" climbed back to 9 percent — matching the peak reached during the Great Recession in 2008. The authors suggest that generalized economic uncertainty may now be reaching even relatively advantaged groups. The post-2014 period encompasses not only continued labor-market precarity but also rising housing costs, student debt burdens, and the political turbulence of the late 2010s, any of which could shake confidence in long-term planning even among women whose incomes alone would seem to secure it.

Intensity told a more dynamic story. Among childless women who intended children, the share reporting weak intentions — saying they would be only a little bothered, or not bothered at all, if they never had a child — rose from 18 percent in 2002 to 26 percent in 2018, a 44 percent increase. The rise was driven almost entirely by young women aged 15 to 29, among whom weak intensity climbed from 17 to 25 percent. Low intensity was also more common among women with less than a bachelor's degree (28 percent in 2018, versus 20 percent for the college-educated) and among women below 200 percent of the poverty line (28 percent, versus 24 percent above it). The pattern echoes recent findings that childless American men are increasingly reporting disinterest in fatherhood, and it aligns with survey evidence that younger cohorts increasingly view parenthood as one acceptable life path among many rather than a default stage of adulthood.

The study then connected these dimensions to the specifics of fertility plans: how many additional children women intended, and when they intended to have the next one. Using regression models controlling for age, partnership status, race and ethnicity, education, employment, income, residence, religiosity, and survey year, the authors found that certainty and intensity were both associated with larger intended family sizes and tighter timelines. Childless women who were "very sure" of realizing their intentions reported intending 2.4 children on average, compared with 2.1 for the "somewhat sure" and 1.9 for the "not at all sure." Those who would be bothered by not having children intended 2.3 children, versus 2.1 for those who would not. The predicted probability of intending a next child within two years was 19 percent for the very sure, 11 percent for the somewhat sure, and 9 percent for the not at all sure, and 16 percent versus 13 percent for intense versus weak intentions. These are associations, not causal estimates, but they suggest that uncertainty and weak commitment are bundled with postponement and smaller intended families — and postponement, in demographic terms, frequently converts into forgone births.

The implications reach beyond measurement. Short-term intentions and intentions with concrete time frames are known to be more predictive of actual childbearing, and quantum intentions underpin U.S. fertility projections produced by statistical agencies and used for planning schools, housing, and social insurance. If high levels of realization uncertainty and low intensity persist even while headline intentions remain stable, aggregate fertility could continue to decline simply because intentions are never carried out. The findings also fit a broader "macro-micro" framework in which economic instability — from the Great Recession onward — makes it harder to plan for children, generating doubt about imagined futures that translates into postponed or abandoned childbearing. The authors note that other uncertainties, including worries about discrimination related to gender identity and sexual orientation, restricted access to reproductive health care, and political and civic disruption, may contribute to what they call "institutionalized uncertainty" surrounding childbearing decisions — a condition in which doubt about the future becomes a normal, expected feature of family formation rather than an exception.

The authors are candid about limitations. They rely on secondary survey data with fixed question wording, which shapes how uncertainty can be measured; the NSFG offers no direct "don't know" option for intentions, so goal uncertainty is likely underestimated. The cross-sectional design cannot track individuals over the life course or establish causal direction — it is possible that women planning children sooner simply feel more certain, rather than certainty producing sooner plans. The NSFG provides no measures of psychological traits or outlooks, no publicly available contextual economic indicators, and no information on male partners' goals, and state-level estimates are not possible. Future work, they argue, will need longitudinal data linking economic conditions, perceived uncertainty, and fertility goals to subsequent behavior.