This Version 1.0 preprint develops a theorem-driven structural account of persistently low birthrates under conditions of concentrated reproductive responsibility. Rather than treating low fertility primarily as a direct expression of preference change, economic cost, cultural decline, or gender-specific behaviour, the paper reframes fertility avoidance as a problem of perceived reproductive feasibility under long-horizon, weakly reversible, responsibility-dense commitment. The argument begins from a minimal set of structural commitments: parenthood constitutes a long-duration and weakly reversible load; voluntary assumption of such load depends on orientation, perceived agency, attainable futures, and sufficient buffering; reproductive responsibility may become concentrated at the couple or household level; and when orientation falls below a feasibility threshold, postponement, stopping, or non-initiation become structurally intelligible responses. From these commitments, the paper derives a wider theorem architecture concerning fertility avoidance, parity progression, policy insufficiency, and cohort-level normalization. The present article develops the fertility-avoidance family in full, specifying theorem statements, observable implications, negative implications, temporal ordering expectations, challenge and falsification conditions, boundary conditions, and downstream empirical instantiation logic. The contribution is structural and diagnostic rather than demographic forecasting, policy advocacy, or empirical estimation. It does not claim that low fertility has a single cause, that economic or gendered constraints are irrelevant, or that individuals consciously reject parenthood. Instead, it specifies what follows when long-horizon reproductive responsibility is experienced as insufficiently carryable under diminished orientation and weakened distributed buffering.
J. E. Fröderberg (Tue,) studied this question.