Health and the Megacity: Urban Congestion, Air Pollution and Birth Outcomes in Brazil

From 2001 to 2009, the number of vehicles in Brazil’s Sao Paulo Metropolitan Area (SPMA) increased from 6 to 9.7 million due to a significant increase in employment rates, ownership of durable goods, average income, and access to credit. This led to dramatic changes in traffic patterns, with SPMA residents spending almost one month each year in traffic. While this type of economic growth often leads to better birth outcomes, increased air pollution from vehicular emissions has also been linked to low birth weight, abnormal deliveries, and preterm birth.  

To evaluate the impact of air pollution in utero, researchers analyzed data from birth records of pregnant women in the Sao Paulo Metropolitan Area during episodes of thermal inversion-meteorological phenomena that exogenously lock pollutants closer to the ground. These served as a proxy for increased air pollution because they have been shown to increase the concentration of particulate matter in cities, and their effect is comparable to an approximately 30% increase in vehicular traffic sluggishness in an area. After identifying thermal inversions using meteorological data, researchers analyzed birth records to identify if there was an association between preterm birth and thermal inversion in the area where the mother resided during her pregnancy.   

Researchers found that an increase of one additional thermal inversion per week during the last 13 weeks of gestation decreases birth weight, increases the chances of prematurity, and greatly affects fetal survival. This research helps clarify the role of increased air pollution on birth outcomes in developing countries that are experiencing rapid economic growth and suggests the need for policies that limit air pollution exposure.  

Methods and Results

Birth data came from individual records in the Brazilian Ministry of Health’s Usage Information System (DATASUS). Brazil’s vital records provide a complete coverage of births: in the mid-2000s, they had a coverage rate above 98% and provide information about newborns’ health, their mothers’ characteristics, and location of residence.  

Researchers used hourly observations of five pollutants (PM10, CO, O3, NOX, and SO2) from air monitoring stations operated by the State of São Paulo’s environmental agency Companhia Ambiental do Estado de São Paulo (CETESB) throughout SPMA and calculated daily average concentrations. To measure whether a thermal inversion occurred, researchers used diurnal vertical temperature profile data collected by CETESB and the University of Wyoming.  

Linking location data for mothers who resided within 20 miles of a weather station in SPMA, researchers found 123 locations of residence and over 3 million live births for analysis from 2002 to 2009. They found that exposure to inversion episodes during the last 13 weeks of gestation increased the incidence of low birth weight by 7.3%, raised the incidence of very low birth weight by 22.5%, increased the chances of prematurity, and greatly affected fetal survival. These results are statistically significant and strongly robust in regard to multiple specification checks, and they are. Overall, the suggestion is that air pollution harms human capital in its earliest stage, in utero, and it may have lasting negative consequences on new generations, requiring local authorities to create environmental regulations and public health initiatives focused on improving prenatal care services.