This paper studies the nexus among fertility, family structure, and gender income equality. I document a novel three-way trade-off in cross-country data: simultaneously achieving high fertility, low single parenthood, and gender income equality is unlikely at all levels of economic development. To explain this fact, I develop a unified theory where the trade-off emerges as an equilibrium outcome. Among various policy instruments, I show that reducing women's child-rearing costs stands out as the unique one that mitigates the trade-off, but the policy costs grow as wages increase. When I calibrate the model to fit Mexico's experience from 1990 to 2015, I find that gender-neutral technological progress explains half of rising single parenthood and declining fertility, while gender-biased productivity growth and the gender education gap reversal account for the narrowing gender income and welfare gaps.