This article waslast modified on November 27, 2017.

a birth defect in which a baby’s head is much smaller than expected and the brain is underdeveloped; this condition can occur because a baby's brain stops developing during pregnancy or stops growing after birth. A more serious, extreme form called severe microcephaly can occur during pregnancy when a baby's brain does not develop properly or begins to develop but then stops. Babies born with microcephaly can have several other issues, such as developmental delays, intellectual disabilities, hearing loss, problems with vision, and seizures.