Puerto Rico does not just have one of the highest preterm birth rates in the United States, it has one of the highest preterm birth rates in the world. Researchers from Northeastern University's Puerto Rico Testsite for Exploring Contamination Threats (PROTECT) Superfund Research Program (SRP) Center, a multi-institution collaboration, may be a step closer to understanding why.
John Meeker, Sc.D., of the University of Michigan, one of the Center's collaborating institutions, led the study. Researchers found that breakdown products of phthalates – chemicals found in food, water, and personal care products – increased the odds of preterm birth in a cohort of pregnant women in Puerto Rico.
Many of the island's 16 active Superfund sites are unlined landfills, and beneath those landfills are drinking water aquifers. These water sources are commonly contaminated with pesticides, heavy metals, and phthalates, creating a potential path for exposure of island residents.
Kelly Ferguson, Ph.D., a former PROTECT SRP trainee and current tenure-track researcher in the NIEHS Epidemiology Branch, collaborated with Meeker on the study.
PROTECT researchers took urine samples from 1,090 women in Puerto Rico at three points during pregnancy and measured different phthalate chemicals. They also analyzed other variables, like maternal age, education level, pre-pregnancy body mass index, and tobacco use, that could contribute to preterm birth. Researchers then looked for associations between exposure to phthalates and gestational age at delivery and increased odds of preterm birth.
In models adjusted for maternal age and education level, urinary concentrations of phthalate breakdown products dibutyl phthalate (DBP) and diisobutyl phthalate (DiBP) were associated with reduced gestational age at delivery and increased likelihood of preterm birth, especially when concentrations were high later in pregnancy. Increased urinary concentrations of DBP and DiBP were associated with 42% and 32% greater odds of preterm birth, respectively, when compared to women with lower exposures.
High preterm birth rates in Puerto Rico may be related to many factors, but this study provides evidence that phthalate exposures may be a contributing factor. According to the authors, this study is, to date, one of the largest and most detailed prospective cohort studies to make associations between breakdown products of phthalates and preterm birth.