In low-fertility societies, and in China in particular after the selective two-child (2013), universal two-child (2016), and three-child (2021) policy relaxations, stated fertility intentions systematically exceed realized childbearing. This problem asks which mechanisms and conditions determine whether stated fertility intentions are actually converted into childbearing: how large the intention–behavior gap is when intention constructs and time horizons are measured consistently with subsequent behavior, which mechanisms (theory-of-planned-behaviour factors, birth-plan making, within-family support and conflict, socioeconomic and institutional constraints, and the policy regime) govern conversion versus intention revision or abandonment, what roles and relative contributions these mechanisms have in the gap, and how far the answer extends beyond two-child-policy-eligible women in Jiangsu and interview samples in Xi'an. The question remains open: the founding studies explain the gap only partially in single-province or single-city samples, the strongest later longitudinal work (Xi'an, 2015–2018) attributes the gap only partly to within-family support, and national evidence through 2021 is descriptive.

Background

Demographers distinguish fertility intentions — stated plans or desires about having (more) children — from realized fertility behavior, and in most low-fertility populations the two diverge: intentions tend to over-predict births. China is an acute case. Its total fertility rate — the average number of children a woman would bear over her lifetime — has been below replacement level (roughly 2.1 children per woman) since the early 1990s (about 1.3 at the 2020 census), and successive policy relaxations — the selective two-child policy (2013/2014), the universal two-child policy (2016), and the three-child policy (2021) — were premised on releasing pent-up childbearing intentions that did not materialize as expected. Understanding why intentions fail to convert into births is therefore central to forecasting and to designing fertility-support policy.

Several frameworks structure the question. The theory of planned behaviour (TPB), a social-psychological model in which behavior follows from intention, which is shaped by attitude toward the behavior, subjective norm (perceived social pressure from significant others), and perceived behavioral control (perceived ease or difficulty of performing the behavior), was applied to Chinese fertility in the Jiangsu Fertility Intention and Behavior Survey (JFIBS), a two-wave longitudinal survey (2007 and 2010) of women in six counties of Jiangsu Province who were eligible to have two children under local birth-planning rules. The resulting study found that even policy-eligible couples decided cautiously about a second child, that attitude, subjective norm, and perceived behavioral control all significantly affect the intention–behavior discrepancy, and that birth-plan making (forming a concrete plan) importantly helps turn intention into behavior — while leaving the conversion mechanism only partially mapped. A related demographic tradition, going back to Bongaarts' decomposition of the gap between reproductive preferences and behavior in post-transitional societies, treats the gap as a structural feature of low fertility rather than measurement noise, and cross-national work shows that intentions are imperfect predictors of realized fertility (in the United States, post-communist Europe, and the countries covered by the Generations and Gender Survey, a large cross-national panel study of family formation). Measurement research adds a caution: fertility 'intentions' range from lifetime family-size ideals to short-term childbearing plans, and gap estimates that compare constructs or time horizons inconsistently (for example, lifetime expectations against recent pregnancy-seeking behavior) misstate both the magnitude and the structure of the gap.

Within China, the empirical base for the conversion question is narrow. Beyond the Jiangsu TPB study, a grounded-theory study — a qualitative method that builds an explanatory model bottom-up through open, axial, and selective coding of interviews — of 27 urban women in Xi'an under the universal two-child policy identified family factors, women's own factors, and social factors as the main drivers of the willingness–behavior difference and explicitly framed both the conversion mechanism and generalization beyond its small sample as open questions. A longitudinal event-history study — a design that models whether and when an event such as a birth occurs — of Xi'an one-child mothers (2015 and 2018 waves) found that only about half of positive second-child intentions produced a birth within three years, and that within-family support and conflict (husband's and firstborn's emotional support, husband's sibship size, firstborn's sex) affected childbearing through channels not fully mediated by intention — explaining the discrepancy only partly. National repeated cross-sectional evidence through 2021 documents trends in the intention–behavior gap but is not longitudinal and identifies no mechanisms. What remains missing is an account, with construct-consistent longitudinal measurement and external validity beyond the founding samples, of which mechanisms and conditions convert stated fertility intentions into childbearing in China's low-fertility, rapidly shifting policy context.

Problem Statement

Determine which mechanisms and conditions govern whether stated fertility intentions are converted into realized childbearing in low-fertility China. The open question encompasses: (1) the magnitude and structure of the fertility intention–behavior gap when the intention construct and its time horizon are measured consistently with the behavioral outcome followed over a matched window (for example, short-term stated childbearing intentions and subsequent births), rather than comparing lifetime ideals or expectations with past or contemporaneous behavior; (2) which mechanisms govern conversion versus intention revision or abandonment, and what roles and relative contributions these mechanisms have in the intention–behavior gap — fertility attitudes, subjective norms, and perceived behavioral control as framed by the theory of planned behaviour; birth-plan formation (forming a concrete implementation intention for when and how to act); within-family support and conflict; socioeconomic and institutional constraints such as income, housing, childcare, and employment; and the surrounding fertility-policy regime (universal two-child, then three-child policy); and (3) how far conclusions extend beyond the founding samples — two-child-policy-eligible women in Jiangsu and urban interview samples in Xi'an. Within part (2), the mechanism classes listed mark the relevant field of mechanisms. The problem is the source question of the Jiangsu theory-of-planned-behaviour study and the Xi'an grounded-theory study, left open by both: not merely measuring the gap, but explaining the conversion of intention into behavior. The founding studies identified significant contributing factors — the Jiangsu analysis found that attitude, subjective norm, and perceived behavioral control significantly affect the discrepancy and that birth-plan making aids conversion, and the Xi'an study modeled family, women's own, and social factors — but each left the conversion mechanism only partially mapped.

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