BACKGROUND: On May 19, 2011, Calgary, Canada stopped fluoridating its drinking water. This prospective ecological study examined if maternal exposure to fluoride during pregnancy from drinking water that was fluoridated at the recommended level of 0.7 mg/L was associated with children's intelligence and executive function at 3-5 years of age.
METHODS: Participants were 616 maternal-child pairs enrolled in the Calgary cohort of the Alberta Pregnancy Outcomes and Nutrition (APrON) study between 2009 and 2012. Maternal-child pairs were classified as fully exposed to fluoridated drinking water throughout pregnancy (n = 295); exposed to fluoridated drinking water for at least part of the pregnancy plus an additional 90 days (n = 220); or not exposed to fluoridated drinking water during pregnancy plus the 90 days prior to pregnancy (n = 101). Children's Full Scale IQs were assessed using the Wechsler Preschool and Primary Scale of Intelligence, Fourth Edition: Canadian (WPPSI-IVCDN). Children's executive functions were also assessed: working memory (WPPSI-IVCDN Working Memory Index), inhibitory control (Gift Delay, NEPSY-II Statue subtest), and cognitive flexibility (Boy-Girl Stroop, Dimensional Change Card Sort (DCCS)).
RESULTS: No associations were found between exposure group and Full Scale IQ. However, compared to no exposure, full exposure to fluoridated drinking water throughout pregnancy was associated with poorer performance on the Gift Delay (B = 0.53, 95 % CI = 0.31, 0.93). Sex-specific analyses revealed that girls in the fully exposed (AOR = 0.30, 95 % CI = 0.13, 0.74) and partially exposed groups (AOR = 0.42, 95 % CI = 0.17, 1.01) performed more poorly than girls in the not exposed group. Sex effects were also found on the DCCS; girls in the fully exposed (AOR = 0.34, 95 % CI = 0.14, 0.88) and partially exposed groups (AOR = 0.29, 95 % CI = 0.12, 0.73) performed more poorly.
CONCLUSION: Maternal exposure to drinking water throughout pregnancy fluoridated at the level of 0.7 mg/L was associated with poorer inhibitory control and cognitive flexibility, particularly in girls, suggesting a possible need to reduce maternal fluoride exposure during pregnancy.

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