Gender equity theories of fertility broadly predict that the lowest fertility in high-income settings will be seen in women facing a 'dual burden' of both paid and unpaid labour responsibilities, but that fertility will increase when male partners share domestic labour. Here we provide a critique of some gender equity theories of fertility in demography, and restate the hypothesis in terms of complementarity between partners. Further, we suggest authors use an interdisciplinary approach, such as integrating perspectives from evolutionary theory and the 'Traits-Desires-Intentions-Behaviour' framework, to provide some consistency to this diverse literature. Building on this theoretical synthesis, we perform a systematic review of 95 pieces of analysis. This broadly supports the idea that fertility will be low where women face a dual burden, which is particularly evident among macro-level studies, micro-level analyses investigating progression to subsequent children, and studies which do not use gender role attitudes as an independent variable.