This study examines the relationship between exposure to violent crime in utero and birth weight using longitudinal data from a household survey conducted in Mexico. Controlling for selective migration and fertility, the results suggest that early gestational exposure to the recent escalation of the Mexican Drug War is associated with a substantial decrease in birth weight. This association is especially pronounced among children born to mothers of low socioeconomic status and among children born to mothers who score poorly on a mental health index.
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The strength of Torche and Villareal’s study is its use of data from the Mexican birth certificate registry. One drawback of this data source, however, is that because of a lack of birth weight information prior to 2008, Torche and Villareal were able to study only a sample in which the majority of the births were conceived after the violent surge had already begun. In addition, the use of administrative data limited the authors’ ability to fully explore or control for systematic fertility and migration responses. Specifically, because it was restricted to using data on births from 2008 to 2010, the analysis of the fertility response has limited information to generate the preescalation of violence trends necessary to fully identify variation in fertility behavior. In the case of the endogenous migration analysis, the use of census data forced the authors to focus on the migration behavior of all women of childbearing age rather than specifically those women giving birth in their sample period. Using the Mexican Family Life Survey, this study will be able to extend the behavioral response analyses in the dimensions mentioned and test the sensitivity of the focal birth weight estimates to explicitly controlling for systematic migratory and fertility behavior.
This sample selection choice also helps alleviate some additional internal and external validity concerns. First, the earliest interviews of MxFLS3 were conducted in August 2009. Thus, the birth records in MxFLS3 are only nationally representative up to July 2009. Second, a large-scale influenza outbreak occurred in Mexico in mid-2009; although not geographically correlated with the violence, this event could still limit the generalizability of the result. Last, although studies on the relationship in Mexico between violent conflict intensity and the level of Great Recession–inspired economic downturn have found no geographic relationship (Ajzenman et al. 2015), reasonable skepticism remains that even if the two events were not initially correlated, they may become intertwined over time (cartels may begin to gravitate toward areas with more or less recession exposure). As such, limiting the sample to those born by July 2009 assists in removing this potential confounding event.
Specifically, 2,880 live births were recorded between MxFLS1 and July 1, 2009 to panel member women in the MxFLS3 reproductive history. I exclude information on 565 of these live births because they represent twins (20), duplicates (5), and nonrepresentative births from years prior to the date being elicited by the reproductive history (540). Thus, the ideal potential sample from the MxFLS if no pertinent information was missing would be 2,315 singleton live births. From this universe of 2,315 live births, I drop 447 observations (19 %) because of missing information on birth weight (100), date of birth (233), or interview date (114).
I calculate the numerator for the outcome birth rate (BR) as the number of births in the MxFLS reproductive history. To create the denominator for the birth rate, I count the number of women aged 14–49 (and thus eligible to complete the reproductive history) in each wave of the MxFLS and considered the base January population in the year following the initiation of that wave of the MxFLS. Then I use a linear imputation method to fill in the months between waves. The period of this analysis runs to June 2009 because this is the latest date for which the MxFLS3 reproductive history is nationally representative.
I also use macrosomia (4,000g and >4,000g) as an independent variable in the main specification, and results provide no evidence that exposure to violence in utero has a relationship with this birth outcome.
Comparing this result with the findings in Mansour and Rees (2012), the magnitude is similar in size (33g) to the decrease in birth weight predicted from experiencing the average first trimester increase in fatalities in the al-Aqsa Intifada. Alternative estimates of the early gestation effect of living in a conflict region would suggest an additional municipal homicide in Mexico has an effect on birth weight that is five times larger (9g) than having a landmine explode in the mother’s municipality of residence in Colombia from 1998–2003 (Camacho 2008) and three times larger (15g) than living in a region of Israel hit by a missile during the 2006 Israel-Hezbollah War (Torche and Shwed 2015). Looking at environmental shocks unrelated to violence, I find that the impact of one additional municipal homicide in early gestation on birth weight is similar in size (51g) to experiencing high-intensity exposure to the 2005 Tarapaca earthquake in Chile in the first trimester (Torche 2011) and approximately double the size (21g) of having a mother’s parent die while in utero (Black et al. 2016).
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Financial support was provided by a T32 Training Grant in the Social, Medical, and Economic Demography of Aging from the National Institute on Aging/National Institutes of Health. I am very grateful to Duncan Thomas, Daniel Rees, Seth Sanders, Erica Field, Elizabeth Frankenberg, V. Joseph Hotz, Alessandro Tarozzi, Andrea Velásquez; three anonymous referees; and participants at the Ninth Annual HiCN Workshop, the Population Association of America Annual Meeting in 2014, the Duke University Population Research Institute seminar series, and the Duke Labor and Development seminar series for their comments and advice while developing this article. I also acknowledge the data collection efforts made by the entire Mexican Family Life Survey team, without which this project would not be possible.
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Brown, R. The Mexican Drug War and Early-Life Health: The Impact of Violent Crime on Birth Outcomes. Demography 55, 319–340 (2018). https://doi.org/10.1007/s13524-017-0639-2