Dec. 30 (UPI) -- Pregnant women may be unknowingly placing their unborn children at risk through exposure to a certain type of pollutants, a study published Monday in the journal JAMA Pediatrics has found.
Research led by the U.S. National Institutes of Health and based on ultrasound scans suggests pregnant women exposed to higher levels of persistent organic pollutants, or POPs, had slightly smaller fetuses than women who weren't exposed to the chemicals.
The results indicate that the chemicals, which are no longer produced in the United States but remain in the environment, may have lasting health effects even at reduced levels.
"The differences we found in fetal growth measures may be more sensitive indicators, compared to birth size, of the potential effects of these compounds," co-author Pauline Mendola, an investigator in the Epidemiology Branch at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, said in a statement. "Even at low levels, there is evidence of a possible effect on fetal growth."
POPs are chemicals like the pesticide DDT and dioxin, a byproduct of herbicide production and paper bleaching. They were used in agriculture, disease control, manufacturing and industrial processes. Though banned worldwide in the late 1990s and early 2000s, they may persist in water and air and may be passed through the food chain.
Earlier research has linked some of these compounds to reproductive disorders and a higher risk of birth defects. However, to Mendola et al, most of these studies looked at infant birth weight and length, measures that could suggest impaired fetal growth but could also indicate genetic factors that lead to smaller birth size and weight.
In addition, many of these studies investigated POPs as individual chemicals, even though people are exposed to a mix of these compounds in the environment.
Mendola and her team analyzed records, stored blood samples and a series of ultrasound scans taken from weeks 16 to 40 in 2,284 pregnant women enrolled in the NICHD Fetal Growth Study from 2009 to 2013. The blood samples were tested for the presence of 76 POPs soon after the women began the study and the POP levels in each woman's blood were listed as percentiles, with the highest levels set at 100 and the lowest at 1.
Then, the researchers compared growth measurements of head circumference, abdominal circumference and thigh-bone length of the fetuses of women in the 75th percentile with those of women in the 25th percentile.
They found that, compared to fetuses in the 25th percentile of exposure, the fetuses of women with exposure in the 75th percentile had the highest growth reductions, with head circumference reduced by an average of 4.7 mm, abdominal circumference reduced by 3.5 mm and femur length reduced by 0.6 mm. In addition, elevated levels of dioxin-like chemicals were associated with an average head circumference reduction of 6.4 mm and an abdominal circumference reduction of 2.4 mm.
Finally, increased levels of flame-retardant chemicals used in furniture, electronics and other consumer products were associated with an average abdominal circumference reduction of 2.4 mm and an average femur length reduction of 0.5 mm.
Notably, the researchers also found that the women in their study had lower levels of POPs than women in the 2003-2004 U.S. Health and Nutrition Survey, the most recent comprehensive study of these compounds in U.S. pregnant women.