In this article, we defend a normative theory of prenatal equality of opportunity, based on a critical revision of Rawls's principle of fair equality of opportunity (FEO). We argue that if natural endowments are defined as biological properties possessed at birth and the distribution of natural endowments is seen as beyond the scope of justice, Rawls's FEO allows for inequalities that undermine the social conditions of a property‐owning democracy. We show this by considering the foetal programming of disease and the possibility of germ‐line modifications. If children of lower socioeconomic background are more likely to develop in a poor foetal environment and germ‐line enhancements are available only to the rich, initial inequalities between the rich and the poor would grow, and yet FEO would be satisfied. In order to avoid the problem, we propose a revised FEO principle omitting any reference to the comparison of natural endowments. Our revised FEO requires that institutions mitigate social class effect from reproduction and gestation to the greatest extent compatible with parental freedoms and the value of the family.