Birth Outcomes after Maternal Exposures to Particulate Matter
August 20, 2012
In response to: Particulate Matter: Widespread and Deadly
Preterm birth is an intractable public health problem affecting more than 500,000 infants per year in the United States1. Other negative birth outcomes closely associated with, but sometimes separate from, preterm birth are low birth weight and small for gestational age. Low birth weight is defined as weighing less than 2500 grams (about 5 pounds, 8 ounces) at birth, while small for gestational age is a designation based on weight norms for babies calculated on how many weeks into the pregnancy they are born. Long-term health effects of preterm birth include intellectual disabilities, cerebral palsy, vision and hearing loss, and respiratory and digestive problems. Low-birth weight babies comprise about 8 percent of all births in the US, and are at increased risk for death in the first year and for serious long-term health problems2. The annual societal economic burden associated with preterm birth in the U.S. was estimated at $26,200,000,000 in 20053.
The dynamics leading to adverse birth outcomes are complex, but are believed to involve a combination of maternal health, genetic and environmental factors. Traditional models of environmental influences examine the effects of nutrition, substance abuse, psychosocial stress and social support on the duration of gestation and newborn weight. A mounting body of research links contaminants in air pollution to preterm birth, low birth weight and small for gestational age. There are several theories why this might be the case, and new research is beginning to shed light on the problem.
Many studies have linked particulate matter in air pollution to preterm, low birth weight, and small for gestational age babies. While information on air pollution’s contribution to adverse birth outcomes can be difficult to compare because of differences in study design, a brief look at recent research reveals persuasive data. Coarse particulate matter (substances between 2.5 - 10 microns in aerodynamic diameter, also known as PM10), and fine particulate matter (less than or equal to 2.5 microns in diameter, or PM2.5), have serious consequences for newborns’ health.
A recent study in North Carolina compared 453,562 birth records with air quality monitoring data. Researchers found a 6.8% higher risk of preterm birth in the mothers who had the highest level of exposure to PM2.5 4. While a study of 164,905 singleton births in Detroit, Michigan did not find an association between maternal particulate matter exposure and preterm birth, researchers did find a correlation between full-term babies born small for gestational age and PM10 5. Researchers in Chicago looked at more than 400,000 birth records and found that PM2.5 was significantly associated with low birth weight even when controlling for other confounding factors6.
Perhaps even more compelling than individual studies are systematic reviews of the literature and meta-analyses of existing data. An International Collaboration on Air Pollution and Pregnancy Outcomes initial report out in summer 2011 looked at statistical methods for evaluating the risk of low birth weight occurring after maternal exposure to PM10. Their analyses suggested decreases in birth weight worsened as PM10 exposure increased7. Another review of sixty-two studies found the majority reported increased odds of low birth weight in relation to exposure to both PM10 and PM2.58. In a third recent review, looking at 41 studies, exposure to PM2.5 was associated with preterm, low birth weight, and small for gestational age births. Exposure to PM10 was associated with small for gestational age births9.
An association between particulate matter exposure during pregnancy and adverse birth outcomes is well supported. There are many possible reasons why this might be the case, including inflammatory changes, decreased oxygenation of the fetus, and toxic effects on the fetus and/or the placenta. Increased blood pressure during pregnancy, known as gestational hypertension, can lead to a life-threatening condition called preeclampsia. In preeclampsia, the mother is in danger of experiencing seizures and multi-organ failure, and the fetus is at risk because of a decrease in the blood and oxygen it receives through the placenta. A study published in July 2012 found first trimester exposures to PM10 were associated with blood pressure changes later in pregnancy10. Another study examining 34,705 singleton births in Pennsylvania found first trimester exposures to PM2.5 were associated with preeclampsia. Smaller increases in risk for gestational hypertension and small for gestational age births were also observed for PM1011. Insight into a possible connection between the chemicals that make up particulate matter and low birth weight is demonstrated in another study out this summer. Potassium and titanium are two chemicals that may be emitted into the air as particulate matter. Researchers looked at the risk of low birth weight following maternal exposure to each of these elements. They found potassium exposure was associated with an 8.75 percent increased risk of low birth weight. Titanium exposure was associated with a 12.1 percent increased risk of low birth weight, with an estimated 6.41 percent increased risk for male babies and 16.4 percent increased risk for females12.
Babies born prematurely, with low birth weight, or small for gestational age face a wide range of health problems. They and their families face a daunting road of complex medical care and intense psychological stress. Exposure to particulate matter during pregnancy is one of many factors contributing to preterm, adverse birth outcomes, but it is a risk factor that can be minimized. Reducing the amount of particulate matter released into the air is a valuable public health strategy for improving infant health.
1. Center for Disease Control & Prevention (2010). Preterm Birth. Retrieved February 9, 2012.
2. March of Dimes (2008). Medical Resources: Low Birthweight. Retrieved February 9, 2012.
3. Board on Health Sciences Policy (2007). Preterm Birth: Causes, Consequences, and Prevention. Retrieved February 9, 2012.
4. Am J Epidemiol. 2012 Jan 15;175(2):91-8. Epub 2011 Dec 13. Time-to-event analysis of fine particle air pollution and preterm birth: results from North Carolina, 2001-2005. Chang HH, Reich BJ, Miranda ML.
5. Environ Int. 2012 Sep;44:7-17. Epub 2012 Feb 6. Air pollutant exposure and preterm and term small-for-gestational-age births in Detroit, Michigan: long-term trends and associations. Le HQ, Batterman SA, Wirth JJ, Wahl RL, Hoggatt KJ, Sadeghnejad A, Hultin ML, Depa M.
6. Atmos Environ. 2012 Mar 1;49:171-179. Uncertainty in the Relationship between Criteria Pollutants and Low Birth Weight in Chicago. Kumar N.
7. Environ Health Perspect. 2011 Jul;119(7):1023-8. Epub 2011 Feb 9. The International Collaboration on Air Pollution and Pregnancy Outcomes: initial results. Parker JD, Rich DQ, Glinianaia SV, Leem JH, Wartenberg D, Bell ML, Bonzini M, Brauer M, Darrow L, Gehring U, Gouveia N, Grillo P, Ha E, van den Hooven EH, Jalaludin B, Jesdale BM, Lepeule J, Morello-Frosch R, Morgan GG, Slama R, Pierik FH, Pesatori AC, Sathyanarayana S, Seo J, Strickland M, Tamburic L, Woodruff TJ.
8. Environ Res. 2012 Jun 20. [Epub ahead of print]. Ambient air pollution, birth weight and preterm birth: A systematic review and meta-analysis. Stieb DM, Chen L, Eshoul M, Judek S.
9. Environ Int. 2011 Feb;37(2):498-516. Epub 2010 Nov 26. Air pollution and birth outcomes: a systematic review. Shah PS, Balkhair T; Knowledge Synthesis Group on Determinants of Preterm/LBW births. Collaborators: Shah PS, Ohlsson A, Shah V, Murphy KE, McDonald SD, Hutton E, Newburn-Cook C, Frick C, Scott F, Allen V, Beyene J.
10. Environ Res. 2012 Jul 24. [Epub ahead of print]. Ambient air pollution exposure and blood pressure changes during pregnancy. Lee PC, Talbott EO, Roberts JM, Catov JM, Bilonick RA, Stone RA, Sharma RK, Ritz B.
11. Matern Child Health J. 2012 Apr 28. [Epub ahead of print]. First Trimester Exposure to Ambient Air Pollution, Pregnancy Complications and Adverse Birth Outcomes in Allegheny County, PA. Lee PC, Roberts JM, Catov JM, Talbott EO, Ritz B.
12. Environ Res. 2012 Jun 15. [Epub ahead of print] Relationship between birth weight and exposure to airborne fine particulate potassium and titanium during gestation. Bell ML, Belanger K, Ebisu K, Gent JF, Leaderer BP.