What Is Microcephaly? A Plain-Language Guide for Parents
Updated: 1 day ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What is microcephaly?
Microcephaly is a rare condition in which an infant's head is much smaller than that of other children of the same age and sex, measured by head circumference on growth charts. It results from problems with brain development, sometimes linked to genetic changes or infections during pregnancy. No treatment enlarges the head, but early speech, physical and occupational therapies help.
What the research says
How common it is: According to PubMed, a CDC-led analysis of 30 U.S. birth defects surveillance programs (births 2009–2013) found a pooled microcephaly prevalence of 8.7 per 10,000 live births. Estimates varied with case definitions and how cases were found. [4]
Where it comes from: A 2025 systematic review of 16 African studies found microcephaly is multifactorial, with Zika virus infection, maternal febrile illness, inadequate antenatal care, HIV exposure, and heavy metal or pesticide exposure all linked. [6]
Surveillance: In 22 U.S. states and territories (2016–2017), areas with widespread Zika transmission had higher rates of nine brain and eye defects, which is why birth defects programs track them. [5]
Europe: Across 24 European registries, prevalence was 1.53 per 10,000 births, ranging from 0.4 to 4.3 per 10,000 between registries, partly because they used different diagnostic cut-offs. [8]
Zika in pregnancy: Among 555 fetuses and infants of mothers with confirmed symptomatic Zika infection, 5.8% had microcephaly (1.6% severe); neurologic and eye defects occurred in 12.7% after first-trimester infection versus 3.6% after second-trimester infection. [9]
1. What is microcephaly?
Microcephaly (my-kroh-SEF-uh-lee) is a rare neurological condition. It means an infant's head is much smaller than the heads of other children of the same age and sex.[1]
It is sometimes detected right at birth. More often, it happens when there is a problem with brain development in the womb, or when the brain stops growing after birth.
Microcephaly can be caused by a variety of genetic and environmental factors. Children with microcephaly often have developmental issues. Although there is no treatment for microcephaly itself, early intervention with speech, occupational, and other supportive therapies may help enhance a child's development and improve quality of life. In the United States, researchers estimate that about 1 in every 1,150 babies has microcephaly.[3]
Head circumference — the distance around the top of the head — is how microcephaly is measured and tracked over time.
2. What does microcephaly look like?
The primary symptom of microcephaly is a head size that is much smaller than that of other children of the same age and sex.[1]
Head size is a measure of the distance around the top of the child's head, called circumference. Using standardized growth charts, healthcare providers compare the measurement with other children's measurements in percentiles.
It helps to know that some children simply have small heads, with a measurement that falls below an established value for children of the same age and sex. In children with microcephaly, the head size measures much smaller than average for the child's age and sex.
A child with more-severe microcephaly may also have a sloping forehead.
3. When should you talk to a doctor about your baby's head?
Chances are your healthcare provider will detect microcephaly at your baby's birth or at a regular well-baby checkup.[1]
However, if you think your baby's head is small for the baby's age and sex, or is not growing as it should, talk to your provider. Early checkups make it easier to understand what is happening and what support your child may need.
Providers measure head circumference at checkups and plot it on growth charts over time to spot microcephaly.
4. What causes microcephaly?
Microcephaly usually is the result of a problem with brain development. This can occur in the womb (congenital) or during infancy. Microcephaly may be genetic.[1]
The following causes have been linked to microcephaly.
Cause | What happens |
Craniosynostosis | The joints (sutures) between the bony plates of the skull fuse too early, keeping the brain from growing |
Genetic changes | Conditions such as Down syndrome may result in microcephaly |
Decreased oxygen to the fetal brain | Pregnancy or delivery complications can impair oxygen delivery to the baby's brain (cerebral anoxia) |
Infections during pregnancy | Toxoplasmosis, cytomegalovirus, rubella (German measles), chickenpox (varicella), and Zika virus can be passed to the fetus |
Drugs, alcohol, or toxic chemicals | Exposure in the womb may affect fetal brain development |
Severe malnutrition | Not getting enough nutrients during pregnancy may hurt fetal brain development |
Uncontrolled PKU in the mother | PKU (phenylketonuria) hampers breaking down the amino acid phenylalanine and may affect the fetus's brain development |
Craniosynostosis (kray-nee-o-sin-os-TOE-sis) deserves a closer look. The early fusing of the joints between the bony plates that form an infant's skull keeps the brain from growing. Treating craniosynostosis usually means an infant needs surgery to separate the fused bones. This surgery relieves pressure on the brain, giving it enough space to grow and develop.[1]
5. Can microcephaly be prevented?
Learning your child has microcephaly can raise questions about future pregnancies. Work with your healthcare provider to determine the cause of the microcephaly.[1]
If the cause is genetic, you may want to talk to a genetics counselor about the risk of microcephaly in future pregnancies.
6. What problems can microcephaly cause?
Some children with microcephaly achieve developmental milestones even though their heads will always be small for their age and sex. But depending on the cause and severity of the microcephaly, complications may include the following.[1]
Possible complication | What it affects |
Developmental delays | Speech and movement |
Coordination and balance | Physical skills and stability |
Dwarfism or short stature | Height and growth |
Facial distortions | Appearance of the face |
Hyperactivity | Attention and behavior |
Intellectual delays | Learning and thinking |
Seizures | Brain activity |
7. How is microcephaly diagnosed?
To determine if your child has microcephaly, your provider likely will take a thorough prenatal, birth, and family history and do a physical exam.[2]
The provider will measure the circumference of your child's head and compare it with a growth chart. Then they will remeasure and plot the growth at future visits. Parents' head sizes also may be measured to determine whether small heads run in the family.
In some cases, particularly if your child's development is delayed, your healthcare provider may order a head CT scan or MRI and blood tests to help determine the underlying cause of the delay.
Care focuses on therapies and support — not on enlarging the head.
8. How is microcephaly treated?
Except for surgery for craniosynostosis, there is generally no treatment that will enlarge your child's head or reverse complications of microcephaly. Treatment focuses on ways to manage your child's condition.[2]
Early childhood intervention programs that include speech, physical, and occupational therapy may help to maximize your child's abilities.
Your healthcare provider might recommend medication for certain complications of microcephaly, such as seizures or hyperactivity.
Treatment approach | What it does |
Surgery (craniosynostosis only) | Separates fused skull bones to relieve pressure and give the brain room to grow |
Speech therapy | Helps the child develop communication skills |
Physical therapy | Helps with movement, coordination, and balance |
Occupational therapy | Helps the child build daily living skills |
Medication | Manages complications such as seizures or hyperactivity |
9. How should parents cope and find support?
When you learn your child has microcephaly, you may feel many different emotions. You may not know what to expect, and you may worry about your child's future. The best remedy for fear and worry is information and support.[2]
Find a team of trusted professionals. You will need to make important decisions about your child's education and treatment. Create a team of healthcare providers, teachers, therapists, and other professionals who can help you evaluate the resources in your area and explain state and federal programs for children with developmental disabilities.
Your child may require care from several medical specialties, including pediatrics and developmental pediatrics, infectious diseases, neurology, ophthalmology, genetics, and psychology.
Seek other families dealing with the same issues. Your community might have support groups for parents of children with developmental disabilities. You might also find online support groups.
10. How should you prepare for your appointment?
If you have just learned your child has microcephaly, or you suspect your child's head is too small, you will likely start by seeing your pediatrician. In some cases, your pediatrician may refer you to a pediatric neurologist.[2]
Before your child's appointment, make a list of symptoms (including any that seem unrelated), key personal information (including major stresses or recent changes), and any medications your child is taking, including vitamins, herbs, and over-the-counter medicines with their dosages.
If you are worried about your child's head size, try to get the hat sizes or measure the head circumferences of several first-degree relatives, such as parents and siblings, for comparison. Take a family member or friend along, if possible, to help you remember the information you are given.
What questions should you ask?
For microcephaly, some basic questions to ask your doctor might include the following.
Question | Why it helps |
What is likely causing my child's symptoms? | Points to the right cause and care plan |
What are other possible causes? | Rules things in or out |
Does my child need additional tests? | Helps you prepare for what comes next |
What is the best course of action? | Clarifies the main treatment path |
What are the alternatives? | Gives you options to weigh |
Is there a treatment that will return my child's head to a more typical size? | Sets honest expectations |
What are the chances my future children will have microcephaly? | Helps with family planning |
Are there brochures or recommended websites? | Gives you reliable reading material |
What will your doctor ask?
Your healthcare professional will likely ask when your symptoms began, whether they have been continuous or occasional, how severe they are, and what, if anything, improves or worsens them.
Conclusion
Microcephaly is a rare condition in which a baby's head is much smaller than the heads of other children the same age and sex. It usually reflects a problem with brain development, whether in the womb or after birth. There is no way to enlarge the head, but surgery can help when early skull fusion is the cause, therapies can help a child build skills, and medicines can manage complications like seizures.
If you are concerned about your child's head size, talk to your pediatrician. Early diagnosis and early intervention make a real difference, and building a trusted team of professionals and connecting with other families can help you feel supported every step of the way.
Learn more. If your baby's head seems small for their age or is not growing as expected, see your pediatrician for a head circumference check. For more plain-language guides on pregnancy, baby development, and childhood conditions, visit Rinnit.com.
Frequently Asked Questions
What is microcephaly?
Microcephaly is a rare condition in which an infant's head is much smaller than the heads of other children of the same age and sex, usually because of a problem with brain development.
How do doctors measure a baby's head?
Doctors measure the head circumference — the distance around the top of the head — and compare it with standardized growth charts using percentiles.
Is microcephaly always present at birth?
Not always. It is sometimes detected at birth, but it can also occur when the brain stops growing after birth.
Can microcephaly be cured or reversed?
There is no treatment that enlarges the head or reverses the condition, except surgery for the specific cause of craniosynostosis. Care focuses on managing the condition through therapies and support.
What infections during pregnancy can cause microcephaly?
Toxoplasmosis, cytomegalovirus, rubella (German measles), chickenpox (varicella), and Zika virus can be passed to the fetus and affect brain development.
Will my child with microcephaly reach normal milestones?
Some children with microcephaly do achieve developmental milestones, though their heads will remain small. The outcome depends on the cause and severity.
Does microcephaly run in families?
Microcephaly can. Microcephaly may be genetic, and parents' head sizes are sometimes measured to see whether small heads run in the family. A genetics counselor can discuss risks for future pregnancies.
Which specialists may care for a child with microcephaly?
A child may need care from pediatrics, developmental pediatrics, infectious diseases, neurology, ophthalmology, genetics, and psychology.
Related Reading
What Is Infant Jaundice? What New Parents Should Know — another common newborn condition parents often ask about.
What Is Infant Acid Reflux? A Plain-Language Guide for Parents — everyday concerns that come up at well-baby checkups.
What Is MCAD Deficiency? A Plain-Language Guide to This Inherited Metabolic Disorder — a rare childhood condition managed with early planning and daily care.
Autism Assessment: Screening Tools, Diagnostic Tests and What to Expect explains how autism is screened for and diagnosed in children and adults.
References
Mayo Clinic Staff. Microcephaly: Symptoms and causes. Mayo Clinic. May 26, 2022. https://www.mayoclinic.org/diseases-conditions/microcephaly/symptoms-causes/syc-20375051
Mayo Clinic Staff. Microcephaly: Diagnosis and treatment. Mayo Clinic. May 26, 2022. https://www.mayoclinic.org/diseases-conditions/microcephaly/diagnosis-treatment/drc-20375056
Centers for Disease Control and Prevention. Microcephaly. CDC. Updated September 23, 2026. https://www.cdc.gov/birth-defects/about/microcephaly.html
Cragan JD, et al. Population-based microcephaly surveillance in the United States, 2009 to 2013: An analysis of potential sources of variation. Birth Defects Res A Clin Mol Teratol. 2016;106(11):972-982. PMID 27891783. https://doi.org/10.1002/bdra.23587
Delaney A, et al. Prevalence of individual brain and eye defects potentially related to Zika virus in pregnancy in 22 U.S. states and territories, January 2016 to June 2017. Birth Defects Res. 2022;114(14):805-811. PMID 35906998. https://doi.org/10.1002/bdr2.2067
Izabayo P, et al. Environmental factors associated with microcephaly in Africa: A systematic review. Neurotoxicol Teratol. 2025;113:107577. PMID 41419017. https://doi.org/10.1016/j.ntt.2025.107577
Boston Children's Hospital. Microcephaly. Boston Children's Hospital. Accessed October 15, 2026. https://www.childrenshospital.org/conditions/microcephaly
Morris JK, Rankin J, Garne E, et al. Prevalence of microcephaly in Europe: population based study. BMJ. 2016;354:i4721. PMID 27623840. https://doi.org/10.1136/bmj.i4721
Hoen B, Schaub B, Funk AL, et al. Pregnancy Outcomes after ZIKV Infection in French Territories in the Americas. N Engl J Med. 2018;378(11):985-994. PMID 29539287. https://doi.org/10.1056/NEJMoa1709481
Medical disclaimer
This article is for informational purposes only and is not medical advice. Always consult a qualified healthcare professional for diagnosis and treatment decisions.
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