Exposure to even moderate amounts of certain pesticides during pregnancy may affect infants' birth size, a new study suggests.
Researchers found that among nearly 500 newborns whose umbilical cord blood was tested for pesticide residues, those with higher levels tended to be smaller at birth.
The chemicals in question include DDT and three other organochlorines—an older group of pesticides that are now banned or restricted in the U.S. and other developed countries, after research linked them to cancer and other potential health risks.
However, the pesticides persist in the environment for years. In the U.S., diet is the main potential source of exposure, according to the Centers for Disease Control and Prevention (CDC)—with fatty foods, like dairy products and oily fish, topping the list.
In the new study, researchers found that for each 10-fold increase in any of the four pesticides in newborns' cord blood, birth weight dipped by roughly 2 to 4 ounces.
Higher levels of DDT were also linked to a decrease in head circumference, while another pesticide—hexachlorobenzene (HCB), once used as a fungicide—was tied to a shorter birth length.
The findings, reported in the journal Pediatrics, do not prove that the pesticides themselves hindered fetal growth.
One problem, the researchers say, is that people are exposed to a "huge variety of chemicals" in the environment, household products and food, for example.
So higher pesticide levels could simply be a marker of higher chemical exposures in general.
In addition, past studies on pesticides and birth size have come to conflicting conclusions, write the researchers, led by Maria-Jose Lopez-Espinosa of the Center for Public Health Research in Valencia, Spain.
Still, they say their findings raise concerns, especially since women in the study appeared to have relatively moderate exposure to pesticides during pregnancy. So the link between pesticides and infants' birth size does not reflect "extreme" exposures, the researchers write.
The findings are based on 494 infants born in Valencia between 2003 and 2006.
When the researchers looked at newborns whose DDT level was above the median, or midpoint, for the group, they found that the infants' head circumference was 0.1 inches smaller versus infants with DDT levels below the median.
When it came to HCB, each 10-fold increase in cord-blood levels was linked to a 0.2-inch decrease in birth length.
All four pesticides were tied to decreases in birth weight. The other two pesticides were DDE (a compound related to DDT) and beta-hexachlorocyclohexane.
While it's not clear that the pesticides are the cause of the birth size differences, it is plausible, according to Lopez-Espinosa's team. The chemicals are thought to interfere with thyroid hormones, which play an important role in growth and development.
According to the CDC, Americans' blood levels of organochlorine pesticides are much lower now than 30 years ago.
In a 2003-2004 government study, most Americans had no detectable amount of DDT and about half had no detectable beta-HCH. On the other hand, most did have detectable DDE which remains in the body longer than DDT as well as HCB.