Associations between Repeated Measures of Maternal Urinary Phthalate Metabolites and Thyroid Hormone Parameters during Pregnancy

Abstract

Background:Maintaining thyroid homeostasis during pregnancy is essential for normal fetal growth and development. Growing evidence suggests that phthalates interfere with normal thyroid function. Few human studies have investigated the degree to which phthalates may affect thyroid hormone levels in particularly susceptible populations such as pregnant women.Objectives:We examined the associations between repeated measures of urinary phthalate metabolites and plasma thyroid hormone levels in samples collected at up to four time points per subject in pregnancy. Additionally, we investigated the potential windows of susceptibility to thyroid hormone disturbances related to study visit of sample collection.Methods:Data were obtained from pregnant women (n = 439) participating in a nested case–control study of preterm birth with 116 cases and 323 controls. We measured 9 phthalate metabolite concentrations in urine samples collected at up to four study visits per subject during pregnancy (median = 10, 18, 26, and 35 weeks of gestation, respectively). We also measured a panel of thyroid function markers in plasma collected at the same four time points per subject during pregnancy.Results:Although our results were generally null, in repeated measures analyses we observed that phthalate metabolites were largely inversely associated with thyrotropin and positively associated with free and total thyroid hormones. Cross-sectional analyses by study visit revealed that the magnitude and/or direction of these relationships varied by timing of exposure during gestation.Conclusions:These results support previous reports showing the potential for environmental phthalate exposure to alter circulating levels of thyroid hormones in pregnant women.Citation:Johns LE, Ferguson KK, McElrath TF, Mukherjee B, Meeker JD. 2016. Associations between repeated measures of maternal urinary phthalate metabolites and thyroid hormone parameters during pregnancy. Environ Health Perspect 124:1808–1815; http://dx.doi.org/10.1289/EHP170

Thyroid hormone parameters during pregnancy in relation to urinary bisphenol A concentrations: A repeated measures study

“…Previous studies of this case-control study population have characterized distributions of BPA and thyroid hormone levels by study visit of sample collection (Cantonwine et al 2015; Johns et al 2016). The overall detection rate of BPA in our study sample was 81.1%.…”

“…The overall detection rate of BPA in our study sample was 81.1%. Geometric means and standard deviations for all thyroid hormones by study visit were calculated and presented in a previous study (Johns et al 2016). In Table 1., we present selected percentiles of BPA concentrations by demographic characteristics.…”

“…In previous studies of this cohort, exposures to environmental phthalates and health outcomes such as preterm birth were investigated (Ferguson et al 2014b), in addition to markers of thyroid function (Johns et al 2016). The initial LifeCodes birth cohort enrolled 1600 women between 2006 and 2008, and of those, 1,181 pregnant women were recruited and followed to term, and delivered live, singleton infants.…”

“…Given that previous analyses of this cohort have investigated the relationship between phthalates and thyroid hormone parameters (Johns et al 2016), we explored the potential influence of phthalates on the relationship between BPA and thyroid hormone parameters. We selected phthalates that were previously shown to be associated with thyroid hormones, and adjusted for individual phthalate metabolites (mono-2-ethylhexyl phthalate [MEHP], mono-iso-butyl phthalate [MiBP], and mono-3-carboxypropyl phthalate [MCPP]) as a covariate in our repeated measures analyses.…”

Effects of Prenatal Phthalate Exposure on Thyroid Hormone Concentrations Beginning at The Embryonic Stage

“…2015 16 observed positive correlations between MBP, MBzP, and mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) and FT4 concentrations in the first trimester of gestation. A repeated measures analysis (median 10, 18, 26, and 35 weeks of gestation) 27 revealed that MEHP and mono-3-carboxypropyl phthalate (MCPP) were positively related to TT4 and FT4, respectively, whereas MEHP, mono-iso-butyl phthalate (MiBP) and MCPP were negatively associated to TSH. Therefore, these findings suggested that the direction of the associations of THs phthalates with THs phthalates varied during pregnancy 27 .…”