Exposure to Air Pollution during pregnancy may curb Fetal Growth

April 12, 2009

Exposure to air pollution during early and late pregnancy may curb the normal growth of the developing fetus, suggests research published ahead of print in the Journal of Epidemiology and Community Health. Pollutants from traffic may be particularly important, the research suggests.

The authors base their findings on singleton births between 1999 and 2003 in the state of New Jersey, USA.

During this period, 492,678 singleton babies were born in New Jersey. After excluding preterm births, and those with incomplete data, almost 336,000 births were included in the analysis.

The researchers used information from birth certificates and hospital discharge records, including the mother's ethnicity, marital status, educational attainment, tobacco use during pregnancy, start of prenatal care, and residence at the time of the birth.

Daily readings of air pollution from monitoring points around the state of New Jersey were retrieved from the US Environmental Protection Agency.

Data from the monitoring point within 10 km (6 miles) of the mothers' homes were used to calculate levels of exposure to average air pollution during each of the three trimesters of the pregnancy, to estimate the associated risk of fetal growth restriction.

They also looked at whether mothers with certain complications of pregnancy were more likely to have restricted baby growth following increases in air pollution late in pregnancy, compared to mothers without these complications.

Mothers of small, and very small birth weight babies were more likely to be younger, less well educated, of African-American ethnicity, smokers, poorer, and single parents than mothers with normal birth weight babies.

But levels of ambient air pollutants were linked to restricted fetal growth, even after taking account of these risk factors.

The risk of a small birth weight baby rose significantly with each increase in particulate matter of 4 ug/m3 during the first and third trimesters of pregnancy.

Similarly, the risk of a very small birth weight baby rose significantly with each 10 parts per billion increase in nitrogen dioxide, suggesting that restricted fetal growth may be linked to traffic pollution or living close to a major road.

Exposure to particulate matter in late pregnancy was also associated with a two to fivefold greater risk of restricted fetal growth among mothers with separation of the placenta before birth and premature rupture of the membrane than in mothers without these complications.

The authors point out that exactly how air pollution might restrict fetal growth is not clear, and its effects may differ between early and late pregnancy and between women with complicated and uncomplicated pregnancies.

But previous research suggests that air pollution might alter cell activity, or cut the amount of oxygen and nutrients a baby receives while in the womb.