Developmental Biology - Persistent Organic Pollutants (POPs)|
Organic Pollutants in Mom's Blood Link to Small Fetus
Pregnant women exposed to persistent organic pollutants, or POPs, have slightly smaller fetuses than women not exposed to these chemicals...
Persistent Organic Pollutants, or POPs, are chemicals once used in agriculture, disease control, manufacturing, and industrial processes. They include the pesticide DDT and dioxin, which is a byproduct of herbicide production and paper bleaching. POPs are slow to break down, may persist in water and air, and can be passed through the food chain.
POPs health effects vary, but some compounds have been linked to reproductive disorders and a higher risk of birth defects.
Pregnant women exposed to POPs had slightly smaller fetuses than women who haven't been exposed to these chemicals, according to an analysis of ultrasound scans by researchers at the National Institutes of Health and other institutions.
Researchers also found women in their study had lower levels of POPs than women in a 2003-2004 U.S. Health and Nutrition Survey, the most recent comprehensive study of such compounds in U.S. pregnant women. These latest findings suggest the chemicals, which are no longer produced in the United States but persist in the environment, may have lasting health effects even at low levels.
The study appears in JAMA Pediatrics and was conducted by Pauline Mendola, Ph.D., an investigator in the Epidemiology Branch at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, and colleagues.
Earlier studies of the potential effects of POP exposure during pregnancy have produced conflicting results. According to the authors, most of these studies looked at infant birth weight and length, measures that could suggest impaired fetal growth but could also indicate genetic factors that lead to smaller birth size and weight. Moreover, previous studies have investigated POPs as individual chemicals, but people typically are exposed to a mix of these compounds.
"The differences we found in fetal growth measures may be more sensitive indicators, compared to birth size, of the potential effects of these compounds. Even at low levels, there is evidence of a possible effect on fetal growth."
Pauline Mendola, PhD
In the current study, researchers analyzed records, stored blood samples, and a series of ultrasound scans taken from weeks 16-40 of 2,284 pregnant women enrolled in the NICHD Fetal Growth Study from 2009 to 2013.
Blood samples were tested for the presence of 76 POPs soon after the women began the study. The POP levels in each woman's blood were listed as percentiles, with the highest levels set at 100 and the lowest at 1. Researchers then compared growth measurements of head circumference, abdominal circumference, and femur (thigh bone) length of the fetuses of women in the 75th percentile to those of women in the 25th percentile.
They found, compared to fetuses in the 25th percentile of exposure to organochlorine pesticides, fetuses of women with exposure in the 75th percentile had the most widespread growth reductions, with head circumference reduced by an average of 4.7 mm, abdominal circumference reduced by 3.5 mm, and femur length reduced by 0.6 mm.
High levels of dioxin-like polychlorinated biphenyls are associated with an average head circumference reduction of 6.4 mm (or 0.251969 inches) and an abdominal circumference reduction of 2.4 mm (or 0.094488189 inches).
High levels of polybrominated diphenyl ethers - flame-retardant chemicals used in furniture, electronics and other consumer products, are associated with (on average) abdominal circumference reduction of 2.4 mm and an average femur length reduction of 0.5 mm .
The importance of Prenatal exposure to persistent organic pollutants (POPs) has been associated with birth size, but data on fetal growth and among racially/ethnically diverse pregnant women remain scarce.
To assess the association between maternal plasma POPs in early pregnancy and fetal growth and by infant sex and maternal race/ethnicity.
Design, Setting, and Participants
This cohort study used the National Institute of Child Health and Human Development Fetal Growth Studies–Singleton cohort, which recruited nonobese, low-risk pregnant women before 14 weeks’ gestation between July 1, 2009, and January 31, 2013, in 12 community-based clinics throughout the United States. Participants self-identified their race/ethnicity, self-reported their behavioral risk factors, and were followed up throughout their pregnancy. Data were analyzed from July 31, 2018, to June 3, 2019.
Levels of 76 POPs in early gestation plasma were measured: 11 perfluoroalkyl and polyfluoroalkyl substances, 1 polybrominated biphenyl, 9 polybrominated diphenyl ethers (PBDEs), 44 polychlorinated biphenyls (PCBs), and 11 organochlorine pesticides (OCPs). The bayesian kernel machine regression method was used to examine chemical class mixtures, and generalized additive mixed model was used to analyze individual chemicals.
Main Outcomes and Measures
Fourteen fetal biometrics were measured, including head circumference, abdominal circumference, and femur length, within 5 ultrasonography appointments.
A total of 2284 low-risk pregnant women were included: 606 women (26.5%) self-identified as white with a mean (SD) age of 30.3 (4.4) years, 589 (25.8%) as black with a mean (SD) age of 25.5 (5.5) years, 635 (27.8%) as Hispanic with a mean (SD) age of 27.1 (5.5) years, and 454 (19.9%) as Asian with a mean (SD) age of 30.5 (4.5) years. A comparison between the 75th and 25th percentile of exposure revealed that the OCP mixture was negatively associated with most fetal growth measures, with a reduction of 4.7 mm (95% CI, -6.7 to -2.8 mm) in head circumference, 3.5 mm (95% CI, -4.7 to -2.2 mm) in abdominal circumference, and 0.6 mm (95% CI, -1.1 to -0.2 mm) in femur length. Higher exposure to the PBDE mixture was associated with reduced abdominal circumference (–2.4 mm; 95% CI, -4.0 to -0.5 mm) and femur length (-0.5 mm; 95% CI, -1.0 to -0.1 mm), and the dioxin-like PCB mixture was associated with reduced head circumference (–6.4 mm; 95% CI, -8.4 to -4.3 mm) and abdominal circumference (–2.4 mm; 95% CI, -3.9 to -0.8 mm). Associations with individual chemicals were less consistent. There were some interactions by fetal sex, although most of the results did not vary by maternal race/ethnicity. For example, oxychlordane (–0.98 mm; 95% CI, –1.60 to –0.36 mm; P for interaction <.001), trans-nonachlor (–0.31 mm; 95% CI, –0.54 to –0.08 mm; P for interaction = .005), and p,p’-dichlorodiphenyldichloroethylene (–0.19 mm; 95% CI, –0.22 to –0.09 mm; P for interaction = .006) were associated with shorter femur length among boys only.
Conclusions and Relevance
This study found that, among pregnant women with low POP levels, a mixture of OCPs was negatively associated with most fetal growth measures and that mixtures of PBDEs and dioxin-like PCBs were associated with reduced abdominal circumference. These findings suggested that, although exposures may be low, associations with fetal growth are apparent.
Marion Ouidir PhD; Germaine M. Buck Louis PhD; Jenna Kanner BS; Katherine L. Grantz MD MS; Cuilin Zhang MD MPH PhD; Rajeshwari Sundaram, PhD; Mohammad L. Rahman MD ScD MPH; Sunmi Lee MA; Kurunthachalam Kannan PhD; Fasil Tekola-Ayele PhD; Pauline Mendola PhD.
Ouidir, M, et al. Association of maternal exposure to persistent organic pollutants in early pregnancy with long-term fetal growth. JAMA Pediatrics. 2019.
About the Eunice Kennedy Shriver National Institute of Child health and Human Development (NICHD): NICHD leads research and training to understand human development, improve reproductive health, enhance the lives of children and adolescents, and optimize abilities for all. For more information, visit http://www.nichd.nih.gov.
About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov
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