While terrorist attacks are relatively infrequent, Gary Becker and Yona Rubinstein (2008) provide evidence that they generate a disproportionate amount of stress and fear, suggesting that the indirect effects may be far more reaching than the direct effects. The international organization Medecins Sans Frontieres (2006) claims that the physiological effect of civil conflict is Colombian’s worst public health problem. This paper is the first attempt to measure the effect of prenatal psychological stress due to terrorism on child birth outcomes. The medical literature indicates that prenatal stress increases levels of CorticotrophinReleasing Hormone (CRH), which regulates the duration of pregnancy and fetal maturation and thus increases the risk of adverse birth outcomes (Pathik D. Wadhwa et al. 1993, among others). There is also evidence that birth outcomes are most sensitive to maternal stress in early stages of pregnancy (Laura M. Glynn et al. 2001). This study finds that the intensity of random landmine explosions during a woman’s first trimester of pregnancy has a significant negative impact on child birth weight. This finding persists when mother fixed effects are included, suggesting that neither observable nor unobservable characteristics of the mothers are driving the results. I use a large dataset, comprising approximately 4 million births in Colombia from 1998 to 2003, which enables me to observe multiple births by the same mother and gives strong statistical power to discern patterns. The data also allow me to link the date of a landmine explosion with the trimester of the pregnancy, and thereby to identify the stage of pregnancy Stress and Birth Weight: Evidence from Terrorist Attacks