Microcephaly is a birth defect that results in a baby’s head being smaller compared to other babies of the same gender and age. In addition, babies with it have smaller brains and may not have developed properly during pregnancy or has stopped developing after birth. State birth defects tracking systems have estimated that microcephaly ranges from 2 babies per 10,000 live births to about 12 babies per 10,000 live births in the Unites States.