The positive impact of fertility decline is not limited to reducing household size, more important, it completely transforms the age structure of the population and provides countries, for a considerable period of time, with a large and growing potentially productive population combined with a shrinking economically dependent population. These advantages make households less vulnerable and provide women with more autonomy in reproductive decision-making, creating a virtuous circle linking demographic trends with socioeconomic progress. The situation is particularly worrying in the case of adolescent girls in Latin America.