Microcephaly can be caused by many disorders, including genetic abnormalities, infections, and brain defects, or can sometimes run in families.
Newborns with severe microcephaly usually have symptoms of brain damage.
Diagnosis is made before birth by doing ultrasound tests or after birth by measuring the head circumference.
Doctors usually do imaging tests to look for brain abnormalities and sometimes blood tests to look for a cause.
Because microcephaly can range from mild to severe, treatment options can range as well.
Early intervention may be especially helpful.
(See also Overview of Brain and Spinal Cord Birth Defects Overview of Brain and Spinal Cord Birth Defects Birth defects of the brain or spinal cord cause a spectrum of neurologic problems; some may be barely noticeable, others may be fatal. Birth defects of the brain and spinal cord can occur in... read more .)
The size of the head is typically determined by the size of the brain. Thus, decreased growth of the brain, or part of the brain, is the cause of microcephaly. Microcephaly can occur alone or in combination with other major birth defects and can be present at birth or develop later in infancy.
Microcephaly is not a common condition.
Causes of Microcephaly
Microcephaly can be caused by a number of disorders, including
Lack of oxygen before or during birth
Certain birth defects of the brain
Infections before birth (such as rubella Rubella Rubella is a contagious viral infection that typically causes in children mild symptoms, such as joint pain and a rash. Rubella can cause death of a fetus or severe birth defects if the mother... read more
, cytomegalovirus Cytomegalovirus (CMV) Infection Cytomegalovirus infection is a common herpesvirus infection with a wide range of symptoms: from no symptoms to fever and fatigue (resembling infectious mononucleosis) to severe symptoms involving... read more , toxoplasmosis Toxoplasmosis Toxoplasmosis is infection caused by the protozoan parasite Toxoplasma gondii. Infection occurs when people unknowingly ingest toxoplasma cysts from cat feces or eat contaminated meat... read more , syphilis Syphilis Syphilis is a sexually transmitted infection caused by the bacteria Treponema pallidum. It can occur in three stages of symptoms, separated by periods of apparent good health. Syphilis... read more 
, or Zika virus Zika Virus Infection Zika virus infection is a mosquito-borne viral infection that typically causes no symptoms but can cause fever, rash, joint pain, or infection of the membrane that covers the white of the eye... read more 
)
Familial microcephaly, in which a smaller head size runs in the child's family, is normally mild and does not cause neurologic symptoms.
Symptoms of Microcephaly
Symptoms depend on how severely the brain is damaged or underdeveloped.
Some of the problems that babies with severe microcephaly can have include seizures Seizures in Children Seizures are a periodic disturbance of the brain’s electrical activity, resulting in some degree of temporary brain dysfunction. When older infants or young children have seizures, they often... read more , developmental delays, feeding problems, hearing or vision problems, problems with movement or balance, hyperactivity, and intellectual disabilities Intellectual Disability Intellectual disability is significantly below average intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily... read more .
Diagnosis of Microcephaly
Before birth, ultrasound
After birth, physical examination and imaging tests
Genetic testing
Before birth, the diagnosis of microcephaly sometimes is made with a routine prenatal ultrasound test Ultrasonography Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more done late in the second trimester or early in the third trimester.
After birth, doctors measure a baby's head circumference Head Circumference Physical growth refers to an increase in body size (length or height and weight) and in the size of organs. From birth to about age 1 or 2 years, children grow rapidly. After this rapid infant... read more (the measurement of the head around its largest area) during routine physical examinations. They diagnose microcephaly when the head circumference is significantly smaller than the normal range for babies of the same sex, age, and ethnic group in the region where the baby lives. Occasionally, the diagnosis is made when the baby's head circumference began in the normal range but is not appropriately increasing as the baby ages.
When making the diagnosis, doctors also take into account the head circumference of the baby's parents because a slightly small head size may run in the family (a condition called benign familial microcephaly).
If microcephaly is present, doctors usually do computed tomography Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more 
(CT) or magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more 
(MRI) of the brain to look for abnormalities. Doctors also evaluate the newborn and parents to look for possible causes of microcephaly and then test for any causes they suspect. Sometimes the doctor may request blood tests to help determine the cause.
A baby who has this birth defect may be evaluated by a geneticist. A geneticist is a doctor who specializes in genetics (the science of genes and how certain qualities or traits are passed from parents to offspring). Genetic testing of a sample of the baby's blood may be done to look for chromosome and gene abnormalities. This testing can help doctors determine whether a specific genetic disorder is the cause and rule out other causes.
Treatment of Microcephaly
Treatment of symptoms
Intervention for physical and intellectual problems
Microcephaly is a lifelong condition, and there is no cure or standard treatment.
Symptoms resulting from brain damage are treated. Some disorders causing microcephaly can be treated.
Regular check-ups and follow-ups by a care team are very important. Developmental services, known as early intervention, often help babies with microcephaly maximize their physical and intellectual abilities.
If a smaller head size runs in the child' family, treatment generally is not necessary.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
March of Dimes: An organization for pregnant people and babies that provides support and information about how to prevent maternal health risks, premature birth, and mother and infant deaths
