Maternal perchlorate levels in the highest 10 % of the population increased the odds of offspring IQ being in the lowest 10 % OR = 3.14 ( 95 % CI 1.38 , 7.13 ) P = .006 with a greater negative impact observed on verbal OR = 3.14 ( 95 % CI 1.42 , 6.90 ) P = .005 than performance IQ .