Pregnant women exposed to harmful chemicals like DDT or dioxin may give birth to smaller children, says study
Pregnant women could risk having smaller infants when exposed to harmful chemicals like DDT or dioxin, finds a new analysis.
These chemicals — persistent organic pollutants (POPs) — were once used in agriculture, disease control, manufacturing, and industrial processes. Though some of the POPs have become obsolete now, they continue to remain in the environment for decades or centuries, posing health problems, suggests the study.
"Findings of this study suggested that maternal exposure to specific persistent organic pollutant mixtures may reduce fetal growth," write the authors of the study. "Even at low levels, there is evidence of a possible effect on fetal growth," says Pauline Mendola, the lead author and an investigator in the epidemiology branch at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development.
This is a cause of concern because infants with impaired growth in the uterus may grow up to have higher chances of developing chronic disease later in life, including metabolic syndrome, obesity, diabetes, hypertension, hyperlipidemia, and complications such as coronary heart disease and stroke, writes Dr Marissa Hauptman from Boston Children's Hospital and Dr Blair J Wylie from the Beth Israel Deaconess Medical Center, in an editorial.
What are POPs?
POPs include pesticides — Aldrin, Dieldrin, Chlordane, organochlorine, DDT, Endrin; industrial chemicals such as Polychlorinated biphenyl (PCB), Hexachlorobenzene (HCB); and some intended byproducts. These chemicals are sturdy and they resist degradation. As a result, they persist in water and air, and may be passed through the food chain — accumulating in the bigger animals as they eat the smaller ones.
These man-made chemicals are found all over the world, even in places far away from industrial sites or from agricultural areas, such as the Arctic circle. POPs travel long distances, as they get picked up by air and ocean currents, according to the World Health Organization (WHO).
POPs can have varying health effects. In animals they are carcinogenic and may cause reproductive and immune problems. In humans, POPs are linked to reproductive disorders and can harm unborn children as well, as they have a higher risk of birth defects.
POPs and birth size
Earlier studies have shown that persistent organic pollutants (POPs) may affect the birth size of fetus. But they have been largely inconsistent, says the study. This is largely due to the fact that these studies have investigated POPs as individual chemicals, but people typically are exposed to a mix of these compounds, according to researchers.
Further, they say, scientists did not know how the chemical's effects on birth size play out among racially or ethnically diverse pregnant women.
To evaluate whether maternal race, ethnicity or infant sex play a role in fetal growth, the team studied 2,284 — white, black, Hispanic, and Asian pregnant women — enrolled in the NICHD Fetal Growth Study from 2009 to 2013. The research team had access to records, stored blood samples, and a series of ultrasound scans of these women taken from weeks 16-40.
From the blood samples, the team looked for the presence of 76 POPs. Some women had higher levels of the chemical than others. Hence, the team listed the varying levels as percentiles, with the highest levels set at 100 and the lowest at 1.
The researchers separated pregnant women with lower blood levels of the chemical, 25th percentile, from the higher 75th percentile. The team then checked growth measurements of head circumference, abdominal circumference, and thigh bone length of the fetuses of women in the 75th percentile to those of women in the 25th percentile.
Among all POPs, researchers found that women exposed to high organochlorine pesticides (75%) had fetuses with the most widespread growth reductions. These fetuses had their head circumference reduced by an average of 4.7 mm, abdominal circumference reduced by 3.5 mm, and thigh bone length reduced by 0.6 mm.
Other POPs had similar effects. For instance, women with high levels of dioxin-like polychlorinated biphenyls had fetuses who showed an average head circumference reduction of 6.4 mm and an abdominal circumference reduction of 2.4 mm. High levels of polybrominated diphenyl ethers — 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 thigh bone length reduction of 0.5 mm.
Their results showed that pregnant women exposed to POPs had slightly smaller fetuses than women who have not been exposed to these chemicals.
The bottom line, according to the research team, is that no chemical that persists in the environment should be introduced in the first place. “Individuals are unlikely to have much agency to control their own exposure and therefore rely on governmental bodies and international agencies to create and enforce policies that restrict use of POPs,” they write.
They suggest that the US government should work with other countries, through the Stockholm Convention 11 or other environmental initiatives, to prevent these persistent toxic chemicals from being produced and released into the environment. “The legacy of these chemicals is often irreversible and has the potential to have deleterious implications for future generations," says the study.
The study has been published in JAMA Pediatrics.