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Perfluorinated acids (PFAs) are widespread global and human blood organohalogen contaminants. These monomer decomposition products used in surface treatment products and in fluoropolymer manufacturing and fire fighting may disrupt maternal thyroid hormone homeostasis given that animal studies demonstrate an apparent hypothyroxinemic condition upon PFA exposure. Firstly, we developed a method for properly quantifying perfluorohexane sulfonate (PFHxS), a PFA suspected of overreporting in past literature. We then investigated whether perfluorooctanoate (PFOA), PFHxS and perfluorooctane sulfonate (PFOS) were determinants of maternal hypothyroxinemia in a pregnant women population from Edmonton using a case-control design. Free thyroxine (fT4) and thyroid stimulating hormone (TSH) were screened in 974 women collected during 15-20 weeks of pregnancy. Cases (n=96, hypothyroxinemic: normal TSH and fT4: lowest 10th percentile) and controls (n=175, fT4: 50th and 90th percentile) were matched based on age and physician. Conditional logistic regression indicated that these PFAs are not associated with maternal hypothyroxinemia. / Environmental Health Sciences