To avoid the risk of preterm birth, pregnant women should avoid personal care products and processed, canned foods that contain the hormone-mimicking group of chemicals known as phthalates (THAL-ates), according to a new study.

Phthalates are found mostly in plastics, where they are used to increase the material’s flexibility and make them more durable. They’re also found in a host of personal-care products, such as deodorants, shampoos, hair gels, hair sprays, nail polishes, and perfumes. As preterm birth marks the leading cause of infant mortality worldwide, researchers sought to better understand the connections between the potentially harmful chemicals, which pregnant women are apt to use rather often, to the risks of delivering a child before the due date.

"For women who are interested in reducing their exposure, reducing use of personal care products, buying phthalate-free [products] when possible, and eating fresher foods may help,” John Meeker, study researcher and associate professor of Environmental Health Sciences at University of Michigan School of Public Health, told LiveScience, “although research on that is limited.”

To perform their study, researchers assembled a group of 130 women in the Boston area who had given birth 37 weeks or earlier (40 weeks is considered full gestation), and 352 women who delivered their baby at full term. The team measured the levels of common phthalates in the women’s urine up to three times during their pregnancy. Women whose urine showed elevated levels of phthalate metabolites displayed a risk of preterm birth that was two to five times higher than women who had lower levels.

Researchers also analyzed the metabolite level in 57 women who had a “spontaneous preterm delivery,” meaning the women didn’t have any underlying medical condition that would explain the preterm birth. Among these women, the team found, metabolite levels were also elevated.

"These data provide strong support for taking action in the prevention or reduction of phthalate exposure during pregnancy," the researchers wrote in their findings.

Because phthalates aren’t chemically bound to the products that contain them, the chemicals can populate the air freely. People expose themselves to phthalates through ingestion, inhalation, and to a lesser extent, through direct dermal contact. According to a 2009 report released by the Centers for Disease Control and Prevention (CDC), phthalates are metabolized and excreted quickly, and do not accumulate in the body. Other research suggests that phthalates may increase oxidative stress and uterine inflammation.

The bulk of scientists’ future work, Meeker noted, concerns the balance between preterm delivery risk worldwide and the sheer pervasiveness of personal-care products. Each year, 500,000 babies are born preterm, according to the CDC. That’s one out of every eight children. In 2009, preterm-related causes of death accounted for 35 percent of all infant deaths. And while the risks dipped slightly in recent years, preterm births have increased by more than a third since 1981. Experts cite increasing maternal age as a factor, along with increased use of assisted reproduction, but a sizable chunk of the preterm births remain unexplained.

In addition to maternal age, factors that increase a woman’s risk for delivering preterm include smoking, alcohol consumption, stress, and high blood pressure.

"There's a list of things phthalates have been shown to do in experimental studies,” Meeker told LiveScience. “Much work is left to be done in human observational studies.”

Source: Ferguson K, McElrath T, Meeker J. Environmental Phthalate Exposure and Preterm Birth. JAMA Pediatrics. 2013.