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Last Edited: 2/20/2009

Infant and Fetal Mortality and the Environment

How are infant and fetal mortality related to the environment?

To what extent should we think about infant and fetal mortality as environmentally-related events?  Since these events are rarer than many outcomes that we study, examining their associations with environmental pollution are more difficult; also, we frequently have a poor understanding of why some infants die, so it is difficult to group them together by cause of death.  In general, we are unable to determine why individual infants may die; what we can do, however, is examine patterns among groups of people to generate hypotheses why the events occur.

One method that researchers use to investigate environmental influences on fetal and infant mortality is to collect samples from mothers (e.g. blood samples); for many substances, one can infer exposure of infants by what is found in samples taken from the mother.  In this way, researchers have noticed that mothers who have experienced stillbirths tend to have higher amounts of DDE (a metabolite of the pesticide DDT) in their bloodstreams.1  The researchers point out, however, that pregnancy and breastfeeding may lower the amount of DDE remaining in mother’s bodies, so it is unclear whether the DDT exposure actually caused stillbirth.

The most common approach used by scientists, however, is to consider where people live during their pregnancy and to relate these locations to estimates of air pollution levels nearby.  The advantage of this approach is that maternal addresses are frequently recorded in birth records, so very large groups of people can be studied for very little cost.  This kind of study has greater limitations, however, since people frequently move residences or spend substantial time away from home during pregnancy. Pollutants nearly always occur in combinations, so it is rarely known whether the compound under study is responsible for the pattern or whether it is a separate substance that may or may not have been measured.  A study located in one city or country will involve different mixtures of pollutants than another, and the populations in question may not be vulnerable in the same way.

Several striking associations of air pollution levels with infant mortality calculated in this way have been noted, however.  Peaks in measured levels of carbon monoxide, sulfur dioxide, nitrogen dioxide, and particulates have been associated with increases in neonatal mortality, postneonatal mortality, and SIDS on the days immediately following.2-4  (Other investigators noted similar patterns but their results were not statistically significant.5, 6).  Other studies consider longer time periods of exposure, such as the first two months of life or the entire lifespan of the infant, suggest similar associations of mortality with exposure.7-12

1.    Longnecker M, Klebanoff M, Dunson D, et al. Maternal serum level of the DDT metabolite DDE in relation to fetal loss in previous pregnancies. Environmental Research. 2005;97:127-133.
2.    Dales R, Burnett R, Smith-Doiron M, Stieb D, Brook J. Air pollution and sudden infant death syndrome. Pediatrics. 2004;113:e628.
3.    Hajat S, Armstrong B, Wilkinson P, Busby A, Dolk H. Outdoor air pollution and infant mortality:  analyis of daily time-series data in 10 English cities. Journal of Epidemiology and Community Health. 2007;61:719-722.
4.    Knöbel H, Chen C-J, Liang K-Y. Sudden infant death syndrome in relation to weather and optimetrically measured air pollution in Taiwan. Pediatrics. 1995;96:1106-1110.
5.    Tsai S-S, Chen C-C, Hsieh H-J, Chang C-C, Yang C-Y. Air pollution and postneonatal mortality in a tropical city:  Kaohsiung, Taiwan. Inhalation Toxicology. 2006;18:185-189.
6.    Yang C-Y, Hsieh H-J, Tsai S-S, Wu T-N, Chiu H-F. Correlation between air pollution and postneonatal mortality in a subtropical city:  Taipei, Taiwan. Journal of Toxicology and Environmental Health, Part A. 2006;69:2033-2040.
7.    Kaiser R, Romieu I, Medina S, Schwartz J, Krzyzanowski M, Künzli N. Air pollution attributable postneonatal infant mortality in U.S. metropolitan areas:  a risk assessment study. Environmental Health. 2004;3:4-9.
8.    Klonoff-Cohen H, Lam P, Lewis A. Outdoor carbon monoxide, nitrogen dioxide, and sudden infant death syndrome. Archives of Disease in Childhood. 2005;90:750-753.
9.    Ritz B, Wilhelm M, Zhao Y. Air pollution and infant death in Southern California, 1989-2000. Pediatrics. 2006;118:493-502.
10.    Woodruff T, Darrow L, Parker J. Air pollution and postneonatal infant mortality in the United States, 1999-2002. Environmental Health Perspectives. 2008;116:110-115.
11.    Woodruff T, Grillo J, Schoendorf K. The Relationship between Selected Causes of Postneonatal Infant Mortality and Particulate Air Pollution in the United States. Environmental Health Perspectives. 1997;105:608-612.
12.    Woodruff T, Parker J, Schoendorf K. Fine particulate matter (PM2.5) air pollution and selected cuases of posteneonatal infant mortality in California. Environmental Health Perspectives. 2006;114:786-790.