Low levels of environmental pollutants may slow fetal growth

(Reuters Health) – Pollutants that persist for decades in the environment may affect fetal growth, a U.S. study suggests.

Even when women had low blood levels of these pollutants, which include substances such as DDT and PCBs, babies’ growth in utero was impacted, researchers report in JAMA Pediatrics.

“These chemicals take a long time to degrade,” said coauthor Pauline Mendola, a senior investigator at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHHD) in Bethesda, Maryland. “Even though most are banned, some for decades, we still see effects.”

The researchers analyzed the impact of mixtures of chemicals since “this is more consistent with the way people are exposed,” she said. “Typically, people are exposed through diet and also drinking water.”

It’s important to regulate chemicals like the ones in the current study “because they don’t go away,” Mendola said. “They persist in the environment and are measurable in humans. And even at very, very low levels of persistent organic pollutants we still saw an effect on fetal growth. We were surprised to see an effect at such low levels of exposure.”

To take a closer look at the possible impact of these persistent man-made chemicals – which include not only pesticides like DDT and PCBs but also flame retardant additives – the researchers turned to data from the NICHHD Fetal Growth studies, which followed a nationwide sample of generally healthy women with low-risk pregnancies, as well as their infants.

Researchers used ultrasound to monitor fetuses, which is a more accurate way to evaluate growth rate than simply measuring a baby’s weight at birth. During the ultrasound exams, numerous fetal measurements were made, including head circumference and femur length.

The 2,284 women included in the current analysis were enrolled during their first trimester and gave a blood sample at that time, which Mendola and her colleagues were able to use to measure pollutant exposure.

The study included a diverse group of women, with 606 identifying as white, 589 as black, 635 as Hispanic and 454 as Asian.

There was some good news: blood pollutant levels were lower in these women than in earlier national samples.

Still, the researchers did find that increasing levels of pollutants in the mother’s blood were associated with increasingly slower growth rates in their fetuses.

For example, when comparing women with the top-25% highest levels of a dioxin-like PCB mixture to women whose levels were in the bottom 25%, the highest levels were associated with 6.5 millimeter (0.26 inch) reduction in fetal head circumference.

Similarly, the highest maternal levels of a mixture of 11 organochlorine pesticides were associated with a 4.7mm reduction in fetal head circumference, a 3.5mm reduction in abdominal circumference and 0.6mm shorter fetal thigh bones.

Right now, it’s not clear what the slower growth rate means in terms of child development, Mendola said.

This is “a really important study,” said Jessie Buckley, an assistant professor in the department of environmental health and engineering at the Johns Hopkins School of Public Health in Baltimore, Maryland. “It’s one of the largest nationwide studies to look at the impact of pollutants on fetal growth rates and it’s looking at mixtures of pollutants. Most studies look at one chemical at a time. But mixtures are what most women are actually exposed to.”

Another strength of the study is the use of ultrasound to measure growth rate rather than birthweight, Buckley said.

As for the significance of slower growth rates, Buckley said, “there are some studies that suggest reduced rate of growth in the uterus can be associated with later-life deficits. It’s something we still need to learn more about.”

Buckley points to fetuses whose mothers smoked during pregnancy. Those babies can end up with a higher risk of obesity when they grow up, she said. “They tend to be growth restricted in utero and they are smaller when they are born,” she added. “They have to do some catchup growing and sometimes they over-catchup and become too big.”

SOURCE: bit.ly/2MKueGC and bit.ly/2SCSEpa JAMA Pediatrics, online December 30, 2019.