The present manuscript provides a definition for, and evaluates the prevalence and maternal/fetal/child impact of, overt hyperthyroidism and overt hypothyroidism. The prevalence of overt hyperthyroidism is 0.5% and the prevalence of overt hyperthyroidism is 0.3%. Overt maternal hyperthyroidism is associated with heart failure, preeclampsia, preterm delivery, still birth, and neonatal mortality. Overt maternal hypothyroidism is associated with preeclampsia, gestational hypertension, cretinism, fetal deaths, and spontaneous abortion. A cost-effective analysis for screening and treating overt thyroid disease during pregnancy is warranted.