Fertility in France to 2040 under additional childbearing postponement: a cohort aligned scenario analysis

Delayed childbearing is an increasingly important reproductive health issue. Beyond its effect on period fertility, postponement shifts childbearing towards ages at which natural fecundity declines and later recuperation may become more constrained. We quantified how additional postponement could affect fertility in France through 2040, distinguishing timing effects from an illustrative assumption of incomplete recuperation. Using the 2026 INSEE central projection, births in 2026–2040 were transported along birth-cohort diagonals using exact annual interval allocation and official female population exposures. Additional postponement was set at zero, 0.5, 1.0, and 1.5 times the observed 2014–2025 increase in mean maternal age (0.08373 years/year). Full recuperation was compared with an illustrative 0.97 multiplier per additional year of delay. Outcomes included total fertility rate (TFR), maternal age, age-specific fertility rates, birth-event accounting, and cumulative cohort fertility through age 40. In 2040, reference TFR was 1.450. At the benchmark postponement rate, TFR decreased to 1.327 with full recuperation and 1.283 with incomplete recuperation; at 1.5 times the benchmark, corresponding values were 1.273 and 1.212. For the 2000 cohort, cumulative fertility through age 40 was 1.484 in the reference versus 1.423 and 1.403 under benchmark postponement. Births deferred beyond 2040 were distinguished from unrecuperated births. Further postponement could substantially reduce fertility observed through 2040 even with full recuperation. Although incomplete recuperation remains assumption-dependent, these findings highlight the reproductive-health relevance of later childbearing and support realistic, non-coercive communication about reproductive ageing and reproductive choices.