Alcohol is now recognized as the most common major destructive environmental agent to which a fetus is likely to be exposed. It is directly responsible for 10-20% of mental deficiency with IQ's in the 50-80 range, and one in six cases of cerebral palsy. Infants with fetal alcohol syndrome tend to exhibit poor growth and have small heads. The average IQ for those with full-blown fetal alcohol syndrome is 63. Affected children tend to be irritable babies and hyperactive children (this hyperactivity can improve over time). They characteristically have short noses and thin, smooth upper lips. Their small upper jaws tend to cause dental problems and repeated ear infections. Small fifth fingernails can be a telltale sign. Cardiac and joint problems are also common. Most of the children with full-fledged fetal alcohol syndrome were born to alcoholic mothers, but milder features of the syndrome are reliably detectable in women who consume as little as two drinks per day.