Causes

Microcephaly usually is the result of abnormal brain development, which can occur in the womb (congenital) or during infancy. Microcephaly may be genetic. Other causes may include:

• Craniosynostosis. The premature fusing of the joints (sutures) between the bony plates that form an infant's skull keeps the brain from growing. Treating craniosynostosis (kray-nee-o-sin-os-TOE-sis) usually means your infant needs surgery to separate the fused bones. If there are no underlying problems in the brain, this surgery allows the brain adequate space to grow and develop.
• Chromosomal abnormalities. Down syndrome and other conditions may result in microcephaly.
• Decreased oxygen to the fetal brain (cerebral anoxia). Certain complications of pregnancy or delivery can impair oxygen delivery to the fetal brain.
• Infections passed to the fetus during pregnancy. These include toxoplasmosis, cytomegalovirus, German measles (rubella), chickenpox (varicella) and Zika virus.
• Exposure to drugs, alcohol or certain toxic chemicals in the womb. Any of these put your baby at risk of brain abnormalities.
• Severe malnutrition. Not getting adequate nutrition during pregnancy can affect your baby's development.
• Uncontrolled phenylketonuria (fen-ul-kee-toe-NU-ree-uh), also known as PKU, in the mother. PKU is a birth defect that hampers the body's ability to break down the amino acid phenylalanine.