In this work we aimed to understand the relationship between alterations in thyroid hormone levels and subsequent impacts on neurodevelopment. We evaluated the epidemiological literature attempting to explore how these alterations would impact potentially sensitive life stages such as fetuses, neonates, breast-fed and bottle-fed infants and the offspring of pregnant women. The majority of the literature located evaluated the relationship between thyroid hormone levels in a pregnant mother and subsequent neurodevelopmental impacts in the offspring. The findings support the concept that the first trimester of pregnancy is likely the most sensitive in regards to adverse neurodevelopmental effects resulting from altered thyroid hormone levels and that free thyroxine is likely the best indicator when evaluating potential adverse neurodevelopmental impacts. Additionally, the results indicate that even subtle alterations of thyroid hormone levels within what is often considered a normal range can have adverse neurodevelopmental impacts. The implications of these findings could pertain to a wide variety of endocrine disrupting chemicals which are known to impact thyroid hormone levels.