A new study has provided preliminary evidence that women with high levels of phthalates, a chemical found in common plastics, in their system during pregnancy were more likely to have low levels of the hormone progesterone, and subsequently develop postpartum depression.

In a paper published April 1 in the Journal of Clinical Endocrinology & Metabolism, a group of epidemiologists investigated the effect that synthetic, harmful chemicals found in everyday household items have on the hormone levels of pregnant women, and how this may impact their mental health. 

Previous studies have shown that the children of women exposed to high levels of phthalates during pregnancy were more likely to have problems with language development and motor skills as they grew. But the current study is the first to examine environmental chemical exposures in relation to postpartum depression, Melanie Jacobson, an environmental and reproductive epidemiologist at the NYU Langone Medical Center and lead author of the paper, told The Academic Times.

Bisphenols are a group of chemical compounds commonly used in polycarbonate plastics and aluminum can lining, and bisphenol A, or BPA, has been used to make plastics and resins for more than 50 years. Phthalates are used as plasticizers, which are substances added to plastics to increase flexibility, transparency, durability and longevity. They are found in thousands of products such as food packaging, toys, lotions, soaps and perfume.

Because of the widespread use of bisphenols and phthalates, discernible levels of them can be detected in the average American adult, including pregnant women. And both chemicals have been proven to be endocrine-disrupting chemicals, which means that they interfere with the body's hormonal processes. 

Jacobson said she designed the study to test the associations between these chemicals and prenatal levels of sex steroid hormones including progesterone, which is critical to pregnancy. Postpartum depression is a serious psychiatric disorder that affects up to 20% of childbearing women, and its causes are multifaceted and not well understood. 

"It has long been hypothesized that [postpartum depression] has an endocrine basis, which means that it is impacted by hormones during pregnancy and postpartum, and hormonal fluctuations," Jacobson said. 

"I thought, if hormones are really important for contributing to postpartum depression, and we know that there are many chemicals in our environment that have been shown to interact with these hormones, specifically during pregnancy, is it plausible that these chemicals could then go on to impact postpartum depression?" she continued.

This study included 139 pregnant adult women who were already participating in the New York University Children's Health and Environment Study, an ongoing clinically enrolled, longitudinal cohort study of pregnant women and their children. 

The researchers measured levels of bisphenols and phthalates in the participants' urine samples during early pregnancy and mid-pregnancy. They also measured sex steroid hormone levels, including pregnenolone, allopregnanolone and progesterone, in blood samples during mid-pregnancy, and assessed the women for postpartum depression symptoms at four months postpartum. Eight types of bisphenols and 22 phthalates were analyzed.

Participants took questionnaires during each trimester of their pregnancy that included socio-demographic information, psychosocial factors, medical history and health behaviors and experiences. Their depressive symptoms during pregnancy were assessed using the Patient Health Questionnaire, a nine-question survey that measures depression. 

Four months after giving birth, the mothers were screened for postpartum depression with the Edinburgh Postnatal Depression Scale, a ten-question survey designed to measure postpartum depression, and they took an additional questionnaire that asked about pregnancy complications, birth outcomes, infant health and their health behaviors and social conditions. 

Twelve women in the sample, or 8.6%, reported scores indicating that they were experiencing postpartum depression. They tended to be older, single and had experienced depressive symptoms during their pregnancy, compared with women who did not experience postpartum depression. Across the sample, pregnenolone and progesterone concentrations tended to decrease with age. Hormone levels also decreased in participants with a higher body mass index.

Bisphenol A was detected in 71% of participants in early pregnancy, and in 76% of the participants in mid-pregnancy. Bisphenol S was detected in 77% of the participants during early pregnancy and in 83% during mid-pregnancy. And of the 22 phthalates assessed, 15 were detected in more than 50% of samples.

Two types of phthalates in particular, di-n-octyl phthalate (DnOP) and diisononyl phthalate (DiNP), were associated with lower prenatal progesterone concentrations and higher postpartum depression symptoms. 

Progesterone regulates the production, release and transport of neurotransmitters, and low levels of this hormone have been linked to anxiety and depression. It also plays an important role in the menstrual cycle and in maintaining the early stages of pregnancy.

In the paper, the authors said that "because phthalate exposure can be reduced through dietary and behavioral interventions such as avoiding food packaging, certain cosmetics and polycarbonate plastic products, these findings provide preliminary evidence identifying prenatal exposure to phthalates as a potentially modifiable risk factor for [postpartum depression]."

Jacobson noted that though the results of the study are intriguing, they should be interpreted with caution. The findings need to be replicated and validated with a larger sample size before any recommendations or concrete claims can be made about plastic, pregnancy and postpartum depression.

Further studies should also investigate whether other phthalates are associated with similar results, and whether there are impacts of these chemicals on gene expression patterns, she suggested.

"While these findings might be somewhat alarming, there actually may be a silver lining because there's something we can do about exposure. Although there are plasticizers all around us in our environment, we can take certain behavior modifications to reduce exposure," Jacobson said.

The study, "Prenatal exposure to bisphenols and phthalates and postpartum depression: The role of neurosteroid hormone disruption," published April 1 in the Journal of Clinical Endocrinology & Metabolism, was authored by Melanie Jacobson, Mengling Liu, Marra G. Ackerman, Jennifer K. Blakemore, Sara E. Long, Kurunthachalam Kannan and Hongkai Zhu, NYU Langone Medical Center; Graziano Pinna and Raquel Romay-Tallon, the University of Illinois at Chicago; Cheryl R. Stein, Hassenfeld Children's Hospital at NYU Langone; and Leonardo Trasande, NYU Langone Medical Center, NYU Wagner School of Public Service and NYU College of Global Public Health.