The relationship between fertility and female labour force participation has been a subject of attention for several decades. Most of the literature focuses on developed countries and responds to the interest in understanding the evolution of the increasing female role in labour markets during the last century and the possible effect that controlled fertility may have on it. Fertility, however, is a choice variable and thus endogenous. Therefore, disentangling its impact is not straight forward and several approaches have been proposed over time in order to isolate it. One of those methods is the use of multiple births occurrence as an instrument for exogenous fertility which was introduced by Rosenzweig and Wolpin (1980) and also used by Bronars and Grogger (1994) and Jacobsen et al. (1999) in the context of developed countries and by Careces-Delpiano (2012) and Ponczek and Souza (2012) for developing countries.