With the onset of the demographic transition in sub-Saharan Africa, couples’ desired number of children and the sex composition of offspring may become conflicted, with potential effects on future fertility. While intuitively expected, this effect has not been observed in studies in sub-Saharan Africa, where the level of fertility is higher than in other African regions. In this study, the hypothesis of a conflicted situation was examined by assessing the effect of sex composition of offspring on women’s intentions regarding additional children and their use of modern contraceptives. A mixed-method analysis was performed using quantitative data regarding 2567 women aged 35–49 years drawn from a 2012 Demtrend retrospective longitudinal population survey, supplemented by qualitative data collected through 23 in-depth interviews of men and women in Ouagadougou. Results showed that the absence of one sex (boy or girl) in the existing offspring was associated with additional demand for children and lower contraceptive use. These results suggest that a desire for a combination of both girls and boys may be the driving factor contributing to larger family size; that is, continued fertility may not be determined by son preference, but rather by overall composition of offspring, when existing children are all girls or all boys. This could explain the stalling of the fertility decline observed in recent years in Ouagadougou.