Microcephaly

How microcephaly is measured

Doctors measure the head circumference around the widest part of the head, above the eyebrows and ears, at birth and at every well-child visit, and plot it on standard growth charts.

• Microcephaly: head size below the 3rd percentile, or more than 2 standard deviations below the average.
• Severe microcephaly: more than 3 standard deviations below the average.

A single small measurement is checked against the baby's length, weight, gestational age and parents' head sizes. Some children have a small head because their parents do, with normal development (familial microcephaly).

Types

• Congenital (primary) microcephaly: present at birth, from problems in brain development during pregnancy.
• Acquired (secondary or postnatal) microcephaly: the head is a normal size at birth but fails to grow normally, often due to brain injury or a genetic condition.

Causes

Genetic

• inherited genes that affect brain growth (primary hereditary microcephaly)
• chromosomal conditions such as Down syndrome and other syndromes
• metabolic disorders, such as untreated phenylketonuria in the mother

Infections during pregnancy

• Zika virus: can cause severe microcephaly and other brain abnormalities (congenital Zika syndrome)
• Cytomegalovirus (CMV): the most common congenital infection in the US
• Toxoplasmosis, rubella, herpes and syphilis

Exposures and other causes

• alcohol use during pregnancy (fetal alcohol spectrum disorder)
• certain drugs and toxins, including mercury and some medicines
• severe maternal malnutrition
• reduced blood or oxygen supply to the baby's brain during pregnancy or birth
• brain injury, stroke or severe infection in early infancy
• craniosynostosis (early fusion of skull bones), which restricts head growth and is treated differently

Signs and effects

Some children have no other problems. Others have one or more of:

• developmental delay in movement, speech and learning
• intellectual disability
• seizures or epilepsy
• problems with movement and balance, sometimes cerebral palsy
• feeding and swallowing difficulties
• hearing loss
• vision problems
• short stature
• hyperactivity

Generally, the smaller the head and the more abnormal the brain on imaging, the more likely significant problems are.

Diagnosis

During pregnancy

Microcephaly can sometimes be seen on a late second or third trimester ultrasound. Fetal MRI and testing for infections or genetic conditions may follow.

After birth

• head measurement and comparison with growth charts over time
• physical examination, including other body features and development
• brain imaging with MRI or CT to look at brain structure
• blood and urine tests for infections, including CMV (best tested in the first 3 weeks of life), Zika and toxoplasmosis
• genetic testing such as chromosomal microarray or exome sequencing
• metabolic tests
• hearing and eye exams

Treatment and support

There is no treatment that makes the head or brain grow to a normal size. Care focuses on helping the child develop and managing health problems:

• early intervention services from birth to age 3, free in the US through state programs
• physical, occupational and speech therapy
• anti-seizure medicines for epilepsy
• feeding support, including nutrition plans and sometimes a feeding tube
• hearing aids and vision support
• antiviral treatment for some babies with congenital CMV, which may help hearing and development
• regular follow-up with a pediatrician, neurologist and developmental specialists
• support for families, including respite care and parent groups

Outlook

Outlook varies widely. Children with mild microcephaly and no other problems may develop normally. Children with severe microcephaly or brain malformations may have lifelong disabilities and medical needs. Life expectancy depends largely on the underlying cause and the severity of associated problems.

Prevention

• avoid alcohol and recreational drugs during pregnancy
• check that rubella (MMR) vaccination is up to date before pregnancy
• avoid travel to areas with active Zika transmission when pregnant, and prevent mosquito bites
• reduce CMV risk by washing hands after changing diapers or wiping a young child's nose, and avoid sharing food, cups or utensils with young children
• avoid raw or undercooked meat and handling cat litter to reduce toxoplasmosis risk
• manage chronic conditions such as phenylketonuria before and during pregnancy

Frequently asked questions

What causes microcephaly?

Microcephaly is caused by problems with brain growth. Causes include genetic conditions, infections during pregnancy such as Zika virus, CMV, toxoplasmosis and rubella, alcohol exposure, severe malnutrition, and lack of oxygen or injury to the developing brain.

Can a baby with microcephaly live a normal life?

Some can. Children with mild microcephaly and no other brain problems may develop normally. Others have developmental delays, seizures or intellectual disability. Early intervention and therapies help each child reach their potential.

Can microcephaly be detected before birth?

Sometimes. It may be seen on ultrasound late in the second trimester or in the third trimester. However, it is often confirmed only after birth by measuring the head circumference.

Is microcephaly treatable?

There is no cure, but many related problems can be treated. Therapies support development, medicines control seizures, and feeding support helps growth. Babies with congenital CMV may benefit from antiviral treatment started early.