We undertook analyses to determine if fetal, intrapartum, and neonatal hypoxia are important causes of low IQ values. We analyzed prospectively collected pregnancy, perinatal, and subsequent developmental data for 19,117 children. As expected, sociohereditary and demographic factors had a large influence on IQ scores. Taking these latter influences into consideration, nothing that happened during labor, delivery, or the neonatal period affected subsequent IQ values. The same was true for early pregnancy disorders that can produce acute fetal hypoxia. By contrast, antenatal disorders and conditions that can produce subacute or chronic fetal hypoxia correlated with low IQ values. These antenatal disorders and conditions were maternal gestational anemia, relative gestational hypotension, hypertension, multiple births, and fetal growth retardation. All of these findings were the same whether neurologic abnormalities were absent or present, suggesting that the same factors were sometimes involved in the genesis of cognitive impairments and neurologic abnormalities.