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Association of maternal urinary fluoride concentrations during pregnancy with size at birth and the potential mediation effect by maternal thyroid hormones: The Swedish NICE birth cohort.
| Environmental Research | Kampouri M, Gustin K, Stravik M, Barman M, Levi M, Daraki V, Jacobsson B, Sandin A, Sandberg AS, Wold AE, Vahter M, Kippler M. |
Thyroid Gland Thyroid Hormones Tissue F Levels Total Body Burden Urine-F Human Study
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Abstract

Highlights

  • Gestational fluoride exposure was associated with increased infant size at birth.
  • Fluoride exposure was linked with increased odds of large for gestational age.
  • Maternal thyroid hormone levels did not explain the observed associations.

Background

Observational studies have indicated that elevated maternal fluoride exposure during pregnancy may impair child neurodevelopment but a potential impact on birth outcomes is understudied.

Objectives

To evaluate the impact of gestational fluoride exposure on birth outcomes (birth size and gestational age at birth) and to assess the potential mediating role of maternal thyroid hormones.

Methods

We studied 583 mother-child dyads in the NICE cohort in northern Sweden. Maternal fluoride exposure was assessed by measuring urinary concentrations at late pregnancy (median: 29th gestational week) using an ion selective electrode. Plasma levels of free and total thyroxine (fT4, tT4) and triiodothyronine (fT3, tT3), and thyroid stimulating hormone (TSH) were measured with electrochemiluminescence immunoassays. The infant’s weight, length, head circumference, and gestational age at birth were extracted from hospital records.

Results

Median urinary fluoride concentration was 0.71 mg/L (5th-95th percentile 0.31–1.9 mg/L; specific gravity adjusted). In multivariable-adjusted regression models, every 1 mg/L increase of maternal urinary fluoride was associated with a mean increase in birth weight by 84 g (95%CI: 30, 138), length by 0.41 cm (95%CI: 0.18, 0.65), head circumference by 0.3 cm (95%CI: 0.1, 0.4), and with increased odds of being born large for gestational age (OR = 1.39, 95%CI: 1.03, 1.89). Every 1 mg/L increase of maternal urinary fluoride was also associated with a mean increase of the plasma fT3:fT4 ratio (B = 0.007, 95%CI: 0.000, 0.014), but not with the hormones or TSH. In mediation analyses, the maternal fT3:fT4 ratio did not explain the urinary fluoride-birth size relationships.

Discussion

Gestational urinary fluoride concentrations were associated with increased size at birth and even with increased odds of being born large for gestational age. The fluoride-related associations with increased size at birth were not explained by changes in maternal thyroid hormone levels.

Appendix A. Supplementary data

The following is the Supplementary data to this article:

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Keywords

urinary Fluoride, Birth weight, Birth length, Birth head circumference, Large for gestational age, Gestational age at birth, Thyroid hormones