CNN  — 

Premature births are on the rise, yet experts aren’t sure why. Now, researchers have found synthetic chemicals called phthalates used in clear food packaging and personal care products could be a culprit, according to a new study.

Past research has demonstrated that phathalates — known as “everywhere chemicals” because they are so common — are hormone disruptors that can impact how the life-giving placenta functions. This organ is the source of oxygen and nutrients for a developing fetus in the womb.

“Phthalates can also contribute to inflammation that can disrupt the placenta even more and set the steps of preterm labor in motion,” said lead author Dr. Leonardo Trasande, director of environmental pediatrics at NYU Langone Health.

“Studies show the largest association with preterm labor is due to a phthalate found in food packaging called Di(2-ethylhexyl) phthalate, or DEHP,” Trasande said. “In our new study, we found DEHP and three similar chemicals could be responsible for 5% to 10% of all the preterm births in 2018. This could be one of the reasons why preterm births are on the rise.”

The 5% to 10% percentage translated into nearly 57,000 preterm births in the United States during 2018, at a cost to society of nearly $4 billion in that year alone, according to the study, published Tuesday in the journal Lancet Planetary Health.

“This paper focused on the relationship between exposure to individual phthalates and preterm birth. But that’s not how people are exposed to chemicals,” said Alexa Friedman, a senior scientist of toxicology at the Environmental Working Group, or EWG, in an email.

“Every day, they’re often exposed to more than one phthalate from the products they use, so the risk of preterm birth may actually be greater,” said Friedman, who was not involved in the study.

The American Chemistry Council, an industry trade association for US chemical companies, told CNN the report did not establish causation.

“Not all phthalates are the same, and it is not appropriate to group them as a class. The term ‘phthalates’ simply refers to a family of chemicals that happen to be structurally similar, but which are functionally and toxicologically distinct from each other,” a spokesperson for the council’s ’s High Phthalates Panel wrote in an email.

Globally, approximately 8.4 million metric tons of phthalates and other plasticizers are consumed every year, according to European Plasticisers, an industry trade association.

Manufacturers add phthalates to consumer products to make the plastic more flexible and harder to break, primarily in polyvinyl chloride, or PVC, products such as children’s toys.

Phthalates are also found in detergents; vinyl flooring, furniture and shower curtains; automotive plastics; lubricating oils and adhesives; rain and stain-resistant products; clothing and shoes; and scores of personal care products including shampoo, soap, hair spray and nail polish, in which they make fragrances last longer.

Studies have connected phthalates to childhood obesity, asthma, cardiovascular issues, cancer and reproductive problems such as genital malformations and undescended testes in baby boys and low sperm counts and testosterone levels in adult males.

“The Consumer Product Safety Commission no longer allows eight dif­ferent phthalates to be used at levels higher than 0.1% in the manufacture of children’s toys and child care products,” Trasande said. “However, not all of the eight have been limited in food packaging by the FDA (US Food and Drug Administration).”

In response to governmental and consumer concerns, manufacturers may create new versions of chemicals that no longer fall under any restrictions. Take DEHP, for example, which has been replaced by newer phthalates called di-isodecylphthalate (DiDP), di-n-octyl phthalate (DnOP), and diisononyl phthalate (DiNP).

Are those safer than the original? That’s not what scientists say they typically discover as they spend years and thousands of dollars to test the newcomers.

“Why would we think that you can make a very minor change in a molecule you are manufacturing and the body wouldn’t react in the same way?” asked toxicologist Linda Birnbaum, former director of the National Institute for Environmental Health Sciences, as well as the National Toxicology Program. She, too, was not involved in the paper.

“Phthalates should be regulated as a class (of chemicals). Many of us have been trying to get something done on this for years,” Birnbaum said in an email.

The new research used data from the National Institutes of Health’s Environmental influences on Child Health Outcomes, or ECHO, study, which investigates the impact of early environmental influences on children’s health and development. In 69 sites around the country, expectant mothers and their newborns are evaluated and provide blood, urine and other biological samples to be analyzed.

The team identified 5,006 pregnant mothers with urine samples that tested positive for different types of phthalates and compared those with the baby’s gestational age at birth, birthweight and birth length.

Data was also pulled from the 2017-2018 National Health and Nutrition Examination Survey, a government program that assesses the health and nutritional status of Americans using a combination of interviews, physical examinations and laboratory analysis of biological specimens.

After analyzing the information, Trasande and his coauthors were able to confirm past research showing a significant association of DEHP with shorter pregnancies and preterm birth.

Interestingly, however, the research team found the three phthalates created by manufacturers to replace DEHP were actually more dangerous than DEHP when it came to preterm birth.

“When we looked further into these replacements, we found even stronger effects of DiDP, DnOP and DiNP,” Trasande said. “It took less of a dose in order to create the same outcome of prematurity.”

A birth is considered preterm if it occurs before 37 weeks of gestation — a full-term pregnancy is 40 weeks or more. Because vital organs and part of the nervous system may not be fully developed, a premature birth may place the baby at risk. Babies born extremely early are often immediately hospitalized to help the infant breathe and address any heart, digestive and brain issues or an inability to fight off infections.

As they grow up, children born prematurely may have vision, hearing and dental issues, as well as intellectual and developmental delays, according to the Mayo Clinic. Prematurity can contribute to cerebral palsy, epilepsy, and mental health disorders such as anxiety, bipolar disorder and depression.

As adults, people born prematurely may also have higher blood pressure and cholesterol, asthma and other respiratory infections and develop type 1 and type 2 diabetes, heart disease, heart failure or stroke.

All of these medical expenses add up, allowing Trasande and his coauthors to estimate the cost to the US in medical care and lost economic productivity from preterm births to be “a staggering $3.8 billion,” said EWG’s Alexa Friedman.

“But the real cost lies in the impact on infants’ health,” Friedman said.

There are additional steps one can take to reduce exposure to phthalates and other chemicals in food and food packaging products, according to the American Academy of Pediatrics’ policy statement on food additives and children’s health.

“One is to reduce our plastic footprint by using stainless steel and glass containers, when possible,” said Trasande, who was lead author for the AAP statement.

“Avoid microwaving food or beverages in plastic, including infant formula and pumped human milk, and don’t put plastic in the dishwasher, because the heat can cause chemicals to leach out,” he added. “Look at the recycling code on the bottom of products to find the plastic type, and avoid plastics with recycling codes 3, which typically contain phthalates.”

CNN’s Jen Christensen contributed to this story.