T3RU and total T4 were determined by radioimmunoassay, and FTi was calculated from T3RU and total [T.sub.4] values (Steuerwald et al.
T3RU is an estimate of the amount of TBG sites unsaturated by [T.sub.4].
The Pearson correlation coefficients between maternal and infant paired serum measures were moderate and statistically significant (p < 0.05) in most cases: [FT.sub.3] (r = 0.31), [FT.sub.4] (0.27), T3RU (0.34), and FTi (0.20).
Most OC concentrations presented in Table 4 showed crude and adjusted inverse associations with T3RU. We observed stronger associations for cord serum T3RU.
The [sigma]PCB coefficients were reduced by about 15% when we adjusted the same models with T3RU as a covariate: Boston Naming scores [-4.77 (-8.45 to -0.99)], 30-month Bayley Motor Scale [-1.50 (-3.46 to 0.46)] and 42-month Bayley Motor Scale [-1.72 (-4.24 to 0.78)].
T3RU showed the strongest positive associations with most of the neuropsychological functions assessed (Table 6).
The present study shows that environmental exposures to OCs, such as PCBs, p,p'-DDE, HCB, and trans-nonachlor, are inversely associated with T3RU during pregnancy and at birth.
Change in test score (expressed as percent of SD) associated with a doubling of T3RU in multiple regression analysis with adjustment for covariates and PCBs.
The T3RU measurement helps estimate the availability of TBG, the protein that carries most of the [T.sub.3] and [T.sub.4] in the blood.
Given the observed data, it is not possible to disentangle whether OCs interact with thyroid binding proteins such as TBG at lower levels of T3RU when the [T.sub.4]/[T.sub.3] binding capacity of serum proteins increases.
The results revealed monotonic and consistent associations between T3RU and some TH levels (i.e., [FT.sub.4] in cord serum) and child neurodevelopment.