Researchers at the National Institutes of Health in the United States have identified a link between exposure to phthalates—chemicals that lend flexibility to many synthetic materials—and a heightened risk of premature birth. The findings were published in The Lancet Planetary Health, underscoring a concern that spans North America and beyond.
To build a clearer picture, the study drew on data from women who took part in the National Children’s Health Environmental Program, a long-running NIH initiative, over a period stretching from 1998 through 2022. The investigative team measured 20 different phthalate metabolites in urine samples collected from participants at several points throughout pregnancy, allowing for a longitudinal view of chemical exposure across gestation. This approach helped scientists trace how varying levels of these metabolites across pregnancy might relate to birth outcomes.
Analysts then examined associations between specific metabolite concentrations in urine and two key birth metrics: infant birth weight and the timing of birth. They also adjusted for a range of known risk factors that can influence preterm birth, including maternal age at delivery and ethnicity. Preterm birth is defined as a birth occurring before 37 weeks of gestation, a threshold linked to later health challenges for newborns.
Among the phthalates detected, monoethyl phthalate and phthalic acid emerged as the most common. These substances are linked to the production of polyester fibers and are widely used in consumer products such as perfumes and soaps. Polyester fibers also serve as structural components in pillows, quilts, and upholstery, while phthalates appear in a broad array of household items, including certain appliances, ballpoint pens, beverage and food packaging, and other everyday goods. The study highlights that ordinary household exposure to these materials may accumulate over time and contribute to measurable differences in birth timing and birth weight.
The analysis identified a notable association with di-2-ethylhexyl phthalate (DEHP). Women with higher levels of DEHP metabolites in their urine prior to delivery were about 45 percent more likely to experience a preterm birth compared with those whose metabolite levels were among the lowest. This magnitude of risk aligns with prior research suggesting that DEHP, a common plasticizer, can interfere with growth and development during pregnancy when exposure is elevated.
Extrapolations from this body of work suggest that population-wide exposure to phthalates could be linked to a meaningful number of preterm births. For the United States in 2018, estimates based on exposure data proposed that tens of thousands of preterm deliveries may have a connection to these chemicals, with implications for health systems, neonatal care, and families. The Canadian and broader North American context is consistent with these concerns, given similar consumer product patterns and environmental exposure pathways in both regions.
The researchers also acknowledged several limitations that temper the findings. Urine measurements capture a snapshot of exposure and may not reflect the total body burden for every individual or tissue. It is possible that participants encountered other phthalate compounds not captured by the specific metabolites tested in this study, and such exposures could modify the observed associations. As with many observational investigations, residual confounding and variations in exposure timing may influence the strength of the reported links between phthalates and birth outcomes.
These results contribute to a growing evidence base about how environmental chemicals interact with pregnancy outcomes. They reinforce the importance of ongoing surveillance and public health strategies aimed at reducing exposure to potentially harmful substances in consumer products, workplaces, and the wider environment. Health agencies and researchers continue to monitor how regulatory actions, product reformulations, and consumer choices can collectively diminish risk and support healthier pregnancies across North America. [Citation: Lancet Planetary Health, 2023–2024, attribution to authors involved in the NIH study and The Lancet Planetary Health report.]