Study question: Are early-pregnancy urinary bisphenol and phthalate metabolite concentrations associated with placental function markers, blood pressure (BP) trajectories during pregnancy and risk of gestational hypertensive disorders?
Summary answer: Early-pregnancy bisphenols and phthalate metabolites were not consistently associated with maternal BP changes or gestational hypertensive disorders, but subclinical, statistically significant associations with placental angiogenic markers and placental hemodynamics were identified.
What is known already: In vitro studies suggest that bisphenols and phthalate metabolites may disrupt early placental development and affect the risk of gestational hypertensive disorders. Previous studies investigating effects of bisphenols and phthalate metabolites on gestational hypertensive disorders reported inconsistent results and did not examine placental function or BP throughout pregnancy.
Study design, size, duration: In a population-based prospective cohort study, bisphenol and phthalate metabolite concentrations were measured in a spot urine sample in early pregnancy among 1396 women whose children participated in postnatal follow-up measurements.
Participants/materials, setting, methods: After exclusion of women without any BP measurement or with pre-existing hypertension, 1233 women were included in the analysis. Urinary bisphenol and phthalate metabolite concentrations were measured in early-pregnancy [median gestational age 13.1 weeks, inter-quartile range 12.1-14.5]. Molar sums of total bisphenols and of low molecular weight phthalate, high molecular weight (HMW) phthalate, di-2-ethylhexylphthalate, and di-n-octylphthalate metabolites were calculated. Placental angiogenic markers (placental growth factor (PlGF), soluble fms-like tyrosine kinase (sFlt)-1), placental hemodynamic function measures (umbilical artery pulsatility index (PI), uterine artery resistance index (RI), notching and placental weight), and maternal BP were measured in different trimesters. Information on gestational hypertensive disorders was obtained from medical records.
Main results and the role of chance: Each log unit increase in HMW phthalate metabolites was associated with a 141.72 (95% CI: 29.13, 373.21) higher early pregnancy sFlt-1/PlGF ratio (range in total sample 9-900). This association was driven by mono-[(2-carboxymethyl)hexyl]phthalate. In the repeated measurements regression models, each log unit increase in bisphenol A was associated with a 0.15 SD (95% CI: 0.03, 0.26) higher intercept and -0.01 SD (95% CI: -0.01, -0.00) decreasing slope of the umbilical artery PI Z-score and a -1.28 SD (95% CI: -2.24, -0.33) lower intercept and 0.06 SD (95% CI: 0.02, 0.11) increasing slope of the uterine artery RI Z-score. These associations remained significant after Bonferroni correction. Early-pregnancy bisphenols or phthalate metabolites showed no consistent associations with any other outcome.
Limitations, reasons for caution: Information on a large number of potential confounders was available but was partly self-reported. Bisphenols and phthalate metabolites, which typically have a half-life of 24-48 h, were measured via single spot urine samples in early-pregnancy. In addition, at the current sample size, the study was powered to detect an odds ratio of 1.57 for gestational hypertension and 1.78 for pre-eclampsia, but was underpowered to perform multivariable analyses for these outcomes. Further studies combining data from different cohorts may be necessary to increase power. These limitations are possible sources of non-differential misclassification leading to bias toward the null.
Wider implications of the findings: Bisphenols and phthalate metabolites were not associated with longitudinal changes in BP in pregnancy in our low-risk population. The observed subclinical associations of phthalates with the sFlt-1/PlGF ratio and of bisphenol A with placental hemodynamics may contribute to adverse pregnancy outcomes. Our results are therefore more supportive of an association of early pregnancy bisphenols and phthalate metabolites with risk for pre-eclampsia than with gestational hypertension.
Study funding/competing interest(s): This analysis was supported by Grant (ES022972) from the National Institutes of Health, USA. The content is solely the responsibility of the authors and does not represent the official views of the National Institutes of Health. The authors report no conflicts of interest.