Hi thank you for posting in HMC, yes hypothyroidism during pregnancy will effect children s I.Q because the fetus alone cannot synthesise its own thyroid hormones for first 12 weeks of pregnancy as its thyroid is in inactive state. Baby completely depends upon mother s thyroid hormones. These hormones play main role in brain development and neurological development. So deficiency of mother s thyroid hormones during pregnancy will lead to problems in children like.. low I.Q, reading and learning disabilities, low school performance, low visual and motor performance. Hope i have answered your question. If you have any further questions i will be happy to help.