Pregnant women who have high levels of chemicals known as phthalates in their urine may have a higher risk of developing postpartum depression, according to a study published in JAMA Psychiatry. Phthalates are used in plastics and personal care products, and they have been identified as chemicals that interfere with normal hormonal actions.

“[T]he withdrawal of estrogen and progesterone after delivery is hypothesized to act as a biological trigger for some forms of [postpartum depression],” wrote Melanie Jacobson, Ph.D., M.P.H., of the NYU Grossman School of Medicine and colleagues. External factors that affect hormones, such as exposure to endocrine-disrupting chemicals, are plausible contributors to postpartum depression, the authors continued, but they have not been sufficiently examined.

Jacobson and colleagues used data from five of the cohorts in the National Institutes of Health’s Environmental Influences on Child Health Outcomes (ECHO) research program from 2006 to 2020. ECHO’s goal is to investigate how prenatal and early life environmental exposures impact child health and development. ECHO studies have taken place across the United States and Puerto Rico. The authors included all pregnant women in the ECHO cohorts for whom data on urinary chemical concentrations from at least one time point in pregnancy were available. The urine samples were analyzed for concentrations of synthetic environmental chemicals found in plastics, including phenols (bisphenol and triclosan), phthalate metabolite, paraben, triclosan, and triclocarban.

Participants also completed postnatal depression assessments between two weeks and 12 months after delivery. For four ECHO cohorts, participants completed the Edinburgh Postnatal Depression Scale, while one cohort completed the Epidemiologic Studies Depression Scale. To make the scores from the two scales comparable, the authors converted patients’ scores to the Patient-Reported Measurement Information System (PROMIS) depression scale.

Among the 2,174 participants included in the study, 349 (16.1%) met the threshold for postpartum depression on the PROMIS scale. These participants were more likely to be Hispanic, from the ECHO cohort in Puerto Rico, have lower education, and have substantially higher prenatal depression scores. Nearly all participants had detectable levels of several phthalate metabolites in their urine samples. The authors did not identify a significant association between environmental chemicals and postpartum depression; however, in further analyses, they found that higher levels of phthalate metabolite concentrations were associated with an increased risk of postpartum depression.

“Given the ubiquitous nature of phthalates in the environment, future studies are needed to confirm these observations,” the authors concluded. “This work underscores the importance of considering pregnancy a critical window of exposure to exogenous agents for maternal health outcomes after delivery, including psychiatric conditions.”