The findings are important because prematurity is a leading cause of infant death around the world, said the report in the Journal of the American Medical Association.
"Our results indicate a significant association between exposure to phthalates during pregnancy and preterm birth," said the study led by Kelly Ferguson of the University of Michigan School of Public Health.
"These data provide strong support for taking action in the prevention or reduction of phthalate exposure during pregnancy."
The study was carried out at Brigham and Women's Hospital in Boston, Massachusetts.
A total of 130 women who gave birth before full term took part, along with 352 control participants.
Researchers analyzed the women's urine samples at different times throughout their pregnancies for levels of phthalate metabolites.
They found that the preterm cases showed "significantly elevated levels" of certain phthalates, including di-2-ethylhexyl phthalate (DEHP), mono-(2-ethyl)-hexyl phthalate (MEHP) and mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP).
The higher the exposure, the more likely it was that the women would give birth too early.
For example, among the women whose concentration of the phthalate metabolite mono-(2-ethyl-5-carboxypentyl) phthalate was above the 75th percentile, the odds ratio for spontaneous preterm birth was 5.23, compared to 2.39 among all preterm births.
Phthalates are commonly found in perfumes, hair spray, nail polish, deodorants, and body lotions.
They are also used in packaging, plastic toys, vinyl, medical supplies and pharmaceuticals.
An accompanying editorial in JAMA by Shanna Swan of Mount Sinai hospital in New York said the research makes an "important public health contribution by demonstrating a sizable impact of phthalates, a class of commonly used chemicals, on a health outcome of major public health concern."
More research is needed to find out if phthalates may be causing the problem by increasing inflammation of the uterus, she wrote.
Some 15 million babies around the world are born preterm, or before 37 weeks in the womb.
Rates have been climbing over the past two decades across the globe, with the highest rates in Southeast Asia, South Asia, and sub-Saharan Africa.
The United States is sixth among the 10 countries with the greatest number of preterm births.
Previous research has found that preterm births are on the rise in the United States, going from a rate of 10.6 percent in 1989 to 12.4 percent in 2004.
"The evidence reported in this new study is strong enough to encourage pregnant women to avoid phthalates if possible, to help minimize their chances of premature birth," said Sarah Robertson, director of The Robinson Institute at the University of Adelaide in Australia.
"The good news is that it's possible to reduce exposure fairly quickly by reading labels and choosing products carefully, using fragrance-free cosmetics, and fresh rather than packaged food."