NIH study finds flame-retardant chemicals may increase risk of preterm birth, higher birth weight

Pregnant individuals exposed to specific classes of flame-retardant chemicals known as organophosphate esters (OPEs) may face an increased risk of preterm birth, especially for baby girls, or higher birth weights for girls and boys, according to a recently published study funded by the Environmental influences on Child Health Outcomes (ECHO) Program at the National Institutes of Health.

Manufacturers commonly use OPEs in products such as furniture, baby items, electronics, clothes, and building materials to prevent fires and make plastics more flexible. People can come into contact with OPEs in various ways, including swallowing or breathing indoor dust or absorbing it through the skin.

In the past decade, OPEs have been increasingly used as flame retardants after polybrominated diphenyl ether (PBDE) flame retardants were phased out due to health risks. ECHO researchers wanted to learn how these now more widespread OPE chemicals might affect pregnancy outcomes such as preterm birth and birth weight.

"The widespread use of products with new flame retardants among pregnant people in the U.S. means that a significant number of births could be affected by these compounds," said Deborah Bennett, PhD, of the University of California, Davis. “In fact, ECHO researchers learned that more than 85% of the study participants had three specific markers of OPE exposure in their bodies.”

Those three substances—diphenyl phosphate (DPHP), a combination of dibutyl phosphate and di-isobutyl phosphate (DBUP/DIBP), and bis(1,3-dichloro-2-propyl) phosphate—were associated with shorter pregnancies and higher risks of preterm birth only among female infants. Among male infants, higher concentrations of DPHP were associated with longer pregnancies.

Babies born to mothers with detectable levels of three other OPE markers—bis(1-chloro-2-propyl) phosphate, bis(2-methylphenyl) phosphate, and dipropyl phosphate—tended to have higher birth weights compared to those whose mothers had no detectable levels of these substances. Babies with a higher birth weight might be more likely to have jaundice, breathing problems, or congenital disorders.

Researchers measured a total of nine OPE markers in urine samples collected from 6,646 pregnant participants across 16 ECHO Cohort Study Sites—often during their third or second trimesters. The researchers assessed birth outcomes, including the length of pregnancy and birth weight, using medical records or parent reports.

“These substances tend to stay in the body for short periods, usually just hours to days,” said Dr. Bennett. “Conducting more thorough studies with various urine tests can help us figure out how they might be linked to birth outcomes.”

Dr. Bennett led this collaborative research published in Environmental Health Perspectives.

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About ECHO: Launched in 2016, the Environmental influences on Child Health Outcomes (ECHO) Program is a research program in the Office of the Director at the NIH with the mission to enhance the health of children for generations to come. ECHO investigators study the effects of a broad range of early environmental influences on child health and development. For more information, visit echochildren.org.

About the NIH: NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information, visit www.nih.gov.