Babies and birth defects

Key Points

Microcephaly may be caused by problems with brain development or being exposed to alcohol and certain drugs, chemicals and infections in the womb.

Zika virus infection during pregnancy causes microcephaly. If you’re pregnant and think you may have Zika, call your health care provider.

Some babies with microcephaly may have lifelong health problems, including intellectual and developmental disabilities.

Treatment for microcephaly depends on your baby’s condition.

What is microcephaly?

Microcephaly is a birth defect in which a baby’s head is smaller than expected, compared to babies of the same sex and age. Babies with mild microcephaly often don’t have problems other than small head size. A baby with severe microcephaly has a head that’s much smaller than expected and may have more serious health problems than babies with mild microcephaly. Severe microcephaly can happen if a baby’s brain doesn’t develop properly during pregnancy or if the brain starts to develop correctly but is damaged during pregnancy.

Birth defects are health conditions that are present at birth. Birth defects change the shape or function of one or more parts of the body. They can cause problems in overall health, how the body develops or how the body works. Some babies have microcephaly along with other birth defects. Microcephaly affects about 2 to 12 in 10,000 babies (less than 1 percent) in the United States.

What causes microcephaly in your baby?

During pregnancy, your baby’s head grows as her brain grows. Microcephaly can happen when a baby’s brain doesn’t develop properly during pregnancy or stops growing after birth. We don’t know for sure what causes microcephaly in most babies. But we do know that these things may cause microcephaly in some babies:

Genes and chromosomes

  • Changes in genes (also called mutations) that affect the brain’s growth and development. This is the most common cause of microcephaly. Genes are part of your body’s cells. They store instructions for the way your body grows and works. Genes are passed from parents to children.
  • Chromosomal conditions, like Down syndrome. Chromosomes are the structures that hold genes. Babies with chromosomal conditions have a problem in one or more of their chromosomes.
  • Untreated maternal PKU. This is a condition passed through genes in which a woman’s body can’t break down an amino acid called phenylalanine. Most women with PKU can have healthy babies if they follow a special meal plan that’s low in phenylalanine.

If your baby’s microcephaly is caused by a gene change or chromosomal condition, you may want to see a genetic counselor. This is a person who is trained to help you understand about genes, birth defects and other medical conditions that run in families, and how they can affect your health and your baby's health.

Exposures in the womb

Brain problems

  • Cerebral anoxia. This is when a baby’s brain doesn’t get enough oxygen. Complications during pregnancy, birth or after birth can cause problems with oxygen flow to a baby’s brain.
  • Craniosynostosis. This is a birth defect in which the joints (also called sutures) between the bones in a baby’s skull fuse together too early, before the brain stops growing. This can cause problems with brain development.
  • Traumatic brain injury. This happens when a head injury causes brain damage.

Metabolism or nutrition problems

  • Metabolic disorders. These are health conditions that affect a body’s metabolism. Metabolism is the way your body changes food into the energy it needs to use oxygen, digest food and grow.
  • Severe malnutrition in the womb. This means a baby doesn’t get enough food or nutrients during pregnancy.

What can you do to help prevent microcephaly in your baby?

You can’t always prevent microcephaly in your baby. But there are things you can do to help reduce your baby’s chances of having it. Here’s how:

  • Don’t drink alcohol. Alcohol includes beer, wine and liquor.
  • Don’t use street drugs or abuse prescription drugs. Tell your provider if you need help to quit using drugs.
  • Protect yourself from harmful chemicals. Wear gloves or a face mask if you have to use them. Open a window or door to let clean air in.
  • If you have PKU, get treatment and follow your meal plan.
  • Protect yourself from infections.

Here’s what you can do to help protect yourself from infections before and during pregnancy:

  • Protect yourself from Zika. Don’t travel to a Zika-affected area unless absolutely necessary. Protect yourself from mosquito bites. If your male or female partner may be infected with Zika, don’t have sex. If you do have sex, use a condom. If you work in a health care setting, follow safety rules to protect yourself from exposure.
  • Talk to your provider to make sure your vaccinations are up to date.
  • Have safe sex to protect you against sexually transmitted diseases (also called STDs) and other infections, including Zika. Safe sex means using a condom if you have sex with more than one partner. If your male or female partner may be infected with Zika, use a condom every time you have sex or don’t have sex at all.
  • Wash your hands often, especially after using the bathroom, sneezing or coughing, changing a diaper or preparing food.
  • Don’t eat raw or undercooked food, including lunch meats. Cook meat, chicken and fish until done. Wash food before you cook or eat it.
  • Don’t touch cat poop or change a cat’s litter box to help protect you from toxoplasmosis.
  • Get regular dental checkups to help prevent gum infections.

How do you know if your baby has microcephaly?

You may find out your baby has microcephaly during pregnancy or after he’s born. During pregnancy, your health care provider may diagnose microcephaly using ultrasound late in the second trimester or early in the third trimester. Ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb.

After birth, a baby with microcephaly may have these signs and symptoms:

  • Small head size
  • Failure to thrive (slow weight gain and growth)
  • High-pitched crying
  • Little appetite or problems with feeding
  • Muscle spasms

To diagnose microcephaly after birth, your baby’s provider measures your baby’s head circumference during a physical exam. Head circumference is the distance around your baby’s head. Your baby’s provider then compares your baby’s measurement to that of other babies of the same sex and age. Visit the Centers for Disease Control and Prevention (CDC) to see growth charts that include head circumference information for babies and children.  He also may do these tests:

  • Blood tests
  • Computed tomography scan (also called CT or CAT scan). CT scan uses special X-ray equipment and powerful computers to make pictures of the inside of your baby’s brain.
  • Magnetic resonance imaging (also called MRI). MRI uses large magnets and radio waves to make a clear picture of your baby’s brain.

What kinds of health problems can babies with microcephaly have?

Some babies with microcephaly have no health complications other than having a small head and being short. But some babies with microcephaly may have long-term or lifelong health problems, including:

  • Cerebral palsy (also called CP). This is a group of conditions that affects the parts of the brain that control muscles. This can cause problems with movement, posture (standing up straight) and balance. 
  • Congenital Zika syndrome. This is a group of health conditions present at birth associated with Zika infection during pregnancy. Congenital Zika syndrome includes birth defects (like microcephaly) and other health and development problems. 
  • Dwarfism or short height. Dwarfism (being a “little person”) is a condition in which a person is very short, less than 4 feet, 10 inches tall as an adult.
  • Face deformities
  • Feeding problems, like trouble swallowing
  • Problems with hearing or vision
  • Hyperactivity (being very active)
  • Seizures
  • Intellectual and developmental disabilities. These are problems with how the brain works that can cause a person to have trouble or delays in physical development, learning, communicating, taking care of himself or getting along with others. Some babies with microcephaly don't reach developmental milestones when expected. A developmental milestone is a skill or activity that most children can do at a certain age. Milestones include sitting, walking, talking, having social skills and having thinking skills.

Babies with severe microcephaly can have more of these problems than babies with mild microcephaly. Severe mirocephaly may be life-threatening. All babies with microcephaly need regular medical check-ups to track their growth and development.

How is microcephaly treated?

There’s no cure for microcephaly. Treatment options depend on how severe your baby’s condition is. Babies with mild microcephaly often don’t have other health problems, but they still need regular check-ups so their health care provider can check their growth and development.

Babies with severe microcephaly may need special care and treatment. Babies with craniosynostosis may need to have surgery to help separate the fused bones in their heads and give the skull the ability to expand as the brain grows and develops.  Some babies need to take medicines to treat seizures or other health problems.

If your baby has microcephaly and has developmental delays, he should see a child neurologist. This is a doctor who treats the brain, spine and nerves in children. Getting early intervention services as soon as possible can help improve your child’s development. These services can help children from birth through 3 years old learn important skills. Services include therapy to help a child talk, walk, learn self-help skills and interact with others. Visit the Early Childhood Technical Assistance Center to find your state’s contact information for early intervention services.

More information

See also: Zika virus and pregnancy

Last reviewed: April, 2017