The demographic transition model predicts that fertility declines as development increases. The proposed mechanisms include: contraceptive access reduces unintended pregnancies, education raises the opportunity cost of child-rearing, and rising income shifts investment from children to capital. When fertility remains high in low-income countries, the standard explanation is constrained access — women would have fewer children if they could.
Dupas, Jayachandran, Lleras-Muney, and Rossi (American Economic Review, 2025) tested this directly. In rural Burkina Faso, 14,545 married women aged 17 to 35 were randomized into a treatment group that received vouchers covering the full cost of all modern contraceptive products and services for three years. The control group received nothing. Additional interventions addressed potential demand-side barriers: correcting misperceptions about child mortality rates and exposing women to different social norms around family size.
The result: no detectable effect on fertility. Free contraception, sustained for three years, combined with informational and social interventions, did not reduce birth rates. The authors could reject even modest effects. The constraint was removed, and nothing changed.
A companion body of evidence compounds the finding. Pooling data from six experimental evaluations across Sub-Saharan Africa, researchers found that development programs that increase women's earnings and household wealth actually increase fertility — particularly among women without a son. Children in this context are not a cost to be reduced but an investment to be funded. More income means more capacity to pursue the family size that was already desired.
The policy framework assumed a constraint model: high fertility reflects limited access and information. The experiment revealed a preference model: high fertility reflects what families want. The intervention removed the assumed constraint without changing the outcome because the constraint was not the cause. The rate was not stuck. It was chosen.