This study examines the union and conception histories of Brazilian women aged 15-49 using the 1996 Demographic and Health Survey’s calendar data. The aim of the paper is twofold: firstly to explore the use of union histories in the DHS calendar data, which have not yet been used for union dynamics studies and secondly to secondly to analyse the relationship between union instability and fertility in Brazil which has been long understudied. Using the example of Brazil it investigates the potential strengths and biases of this data source. In particular it analyses the impact of union dissolution on fertility in Brazil using multiprocess event history analysis techniques as developed by Lillard (1993). This type of methodology has been widely used for the analyses of developed countries data. However, it has not been explored for developing countries mainly due to the lack of data. The paper will demonstrate the positive effect of union instability on fertility.