Female labor force participation rates across the Middle East and North Africa (MENA) region have remained low for over four decades, despite the fact that in the same period, women's education rapidly increased and fertility rates substantially decreased. This surprising phenomenon has remained a puzzle. This study tries to provide a better understanding of this puzzle by testing whether there is a causal impact of the number of children on mother's labor supply. It uses twins at first birth as an instrumental variable to estimate the causal impact of fertility on participation of mothers in the labor market, free of bias. It finds that having more children does not reduce women's employment. The paper discusses the implications of this interesting result in understanding the puzzle of female participation in MENA and in designing policies to increase women's work.