By Margarita Nahapetyan
According to the U.S. scientists, exposure to air pollution during pregnancy may harm and affect the development of babies in the womb. The study, one of the largest to look at the effect of air pollution on pregnancy, found that future moms-to-be who inhale polluted air during the first three months and the third trimester of pregnancy, are at higher risk of delivering a child with low weight.
The findings are based on the study of 336,000 babies born in New Jersey, USA, between 1999 and 2003. Daily readings from monitoring points within 6 miles of the mothers' homes were used to calculate average levels of air pollution during their pregnancies. The readings were taken from the U.S. Environmental Protection Agency.
For the study, the researchers from the University of Medicine and Dentistry in New Jersey, collected data from birth certificates and hospital notes. The information on twins or other multiple births was not considered, the experts only looked at data on babies identified as white, African-American or Hispanic. After that they recorded factors such as each mother's age, ethnicity, marital status, education level, her smoking and alcohol use habits - as well as where she lived when her child was born. The researches got even more information about the pregnancy from the hospital discharge records, in particular, about complications known to affect fetal growth. They estimated the duration of the pregnancy based on the date of the last known menstrual period and clinical judgment, rather than an ultrasound scan.
The results showed that mothers of babies with small, and very small birth weight, were more likely to be younger, less well educated, of African-American ethnicity, smokers, poorer, and single parents compared to mothers who delivered babies with normal birth weight. However, even after taking into consideration all these factors, higher levels of air pollutants were associated with restricted fetal growth.
One of the harmful pollutants was PM 2.5 particulate matter - tiny specks of sooty chemicals with 2.5 micrometers or less in diameter. Particulate matter is produced from vehicle exhausts and can settle in the lungs. Fine particles, such as PM 2.5s, which penetrate deep into the lungs, have been associated with deaths from heart-related and respiratory diseases.
The scientists found that in the first three and the last three months of pregnancy, the chance of having a "small for gestational age" (SGA) child, rose significantly with higher levels of PM 2.5. The risk rose by more than 4 per cent for every PM 2.5 increase of four micrograms per cubic meter of air. Similarly, there was an association between the risk of a very small birth weight baby and nitrogen dioxide concentrations. At all stages of pregnancy, the risk of having a "very small for gestational age" (VSGA) child, increased by more than 7 per cent with each 10 parts per billion increase in nitrogen dioxide.
SGA babies were defined as being between 75 per cent and 85 per cent of normal size. VSGA babies were at least 75 per cent smaller than normal. The study also found that exposure to particulate matter in later pregnancy was associated with a 2- to 5-fold increased risk of restricted fetal growth among mothers with pregnancy complications such as separation of the placenta before birth and premature rupture of the membrane, compared with mothers who did not have these complications.
"Our findings suggest that air pollution, perhaps specifically traffic emissions during early and late pregnancy and/or factors associated with residence near a roadway during pregnancy, may affect foetal growth," the scientists wrote. They said it is not clear yet how exactly air pollution might restrict foetal growth, but they add that some previous studies have shown that air pollution might alter cell activity, or cut the amount of oxygen and nutrients a child receives while in the womb.
The findings are published in the latest issue of the Journal of Epidemiology and Community Health.