My Baby's Head Seems Too Small (Microcephaly)
Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist
Content reviewed against published CDC, AAP, WHO guidelines
Last reviewed:
If your baby has been diagnosed with or you suspect head seems too small (microcephaly), here is what the evidence says.
The short answer
A baby's head circumference is measured at every well-child visit to track brain growth. A head that is smaller than expected does not always mean there is a problem - genetics play a major role, and some families naturally have smaller head sizes. However, if the head circumference is significantly below normal or is falling off its growth curve, your pediatrician will want to investigate further.
Key takeaways
- A baby's head circumference is measured at every well-child visit to track brain growth. A head that is smaller than expected does not always mean there is a problem - genetics play a major role, and some families naturally have smaller head sizes. However, if the head circumference is significantly below normal or is falling off its growth curve, your pediatrician will want to investigate further.
- Usually normal when: Your baby's head circumference is below average but tracking consistently along its percentile curve
- Call your doctor if: Your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills
- Varies by age — see the age-by-age breakdown below
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What Parents Should Know
According to CDC, AAP, WHO guidelines, a baby's head circumference is measured at every well-child visit to track brain growth. A head that is smaller than expected does not always mean there is a problem - genetics play a major role, and some families naturally have smaller head sizes. However, if the head circumference is significantly below normal or is falling off its growth curve, your pediatrician will want to investigate further. At 0-1 month, head circumference is measured at birth and compared to gestational age. Microcephaly is defined as a head circumference more than 2 standard deviations below the mean for age and sex. Primary (congenital) microcephaly is present at birth and can result from genetic conditions, prenatal infections (such as Zika, CMV, or toxoplasmosis), or prenatal exposure to alcohol or certain medications. Molding from birth can temporarily affect measurements, so repeat measurements are important. It is generally considered normal when your baby's head circumference is below average but tracking consistently along its percentile curve. However, you should contact your pediatrician promptly if your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills.
Normal vs. Concerning
By Age
What to expect by age
0-1 month
Head circumference is measured at birth and compared to gestational age. Microcephaly is defined as a head circumference more than 2 standard deviations below the mean for age and sex. Primary (congenital) microcephaly is present at birth and can result from genetic conditions, prenatal infections (such as Zika, CMV, or toxoplasmosis), or prenatal exposure to alcohol or certain medications. Molding from birth can temporarily affect measurements, so repeat measurements are important.
1-6 months
During the first year, the brain grows rapidly, and head circumference should increase at a predictable rate. If the head circumference is tracking along a low but consistent percentile, and the baby is developing normally, this may simply reflect familial (genetic) patterns - measuring parents' head circumferences can be informative. However, if the head circumference is crossing percentile lines downward, this suggests the brain growth is slowing and warrants evaluation with imaging and possibly genetic testing.
6-12 months
Secondary (acquired) microcephaly develops after birth and involves a head circumference that was initially normal but has progressively fallen below expected levels. This can be caused by oxygen deprivation, infections (such as meningitis), metabolic disorders, or genetic conditions that manifest later. Your pediatrician will track the growth curve carefully. If developmental delays are also present, a comprehensive evaluation including brain imaging (MRI), genetic testing, and developmental assessment is important.
12 months+
Head growth continues but at a slower rate after the first year. If your child has confirmed microcephaly, the focus shifts to supporting development and addressing any associated conditions. Many children with mild microcephaly develop normally or with minimal issues, while severe cases may be associated with intellectual disability, seizures, or other neurological challenges. Early intervention services can be extremely beneficial.
What to Tell Your Pediatrician
- Describe when you first noticed head seems too small (microcephaly) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby's head circumference has crossed downward across two or more percentile lines on the growth chart.
- Mention if you are concerned that your baby's head looks disproportionately small compared to their body.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- Your baby's head circumference is below average but tracking consistently along its percentile curve
- Both parents have smaller than average head sizes (familial microcephaly)
- Your baby is meeting developmental milestones on time and is otherwise healthy
- A single measurement was low but subsequent measurements show normal growth velocity
- Your baby's head circumference has crossed downward across two or more percentile lines on the growth chart
- You are concerned that your baby's head looks disproportionately small compared to their body
- Your baby has developmental delays or unusual neurological symptoms along with a small head
- Your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills
- Your newborn's head circumference is more than 3 standard deviations below the mean, as this warrants urgent brain imaging and evaluation
What You Can Do at Home
- Keep track of when you notice head seems too small (microcephaly) — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that your baby's head circumference is below average but tracking consistently along its percentile curve — this is generally within the range of normal.
- At 0-1 month, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
- While monitoring at home, seek immediate care if your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills.
Related Resources
Growth Percentile Calculator
Plot your baby's weight, length, and head circumference on WHO/CDC growth charts.
Month-by-Month Development
Detailed monthly development guides from birth through 24 months.
When to Call the Doctor
General guide on when to call the pediatrician, visit urgent care, or go to the ER.
Frequently asked questions
Is head seems too small (microcephaly) normal?
When should I call the doctor about head seems too small (microcephaly)?
When is head seems too small (microcephaly) normal?
What causes head seems too small (microcephaly)?
What should I mention to my pediatrician about head seems too small (microcephaly)?
Is head seems too small (microcephaly) normal at 0-1 month?
Is head seems too small (microcephaly) normal at 1-6 months?
Should I go to the ER for head seems too small (microcephaly)?
Does head seems too small (microcephaly) go away on its own?
References
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss My Baby's Head Seems Too Small (Microcephaly).
Things to mention
- Describe when you first noticed head seems too small (microcephaly) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby's head circumference has crossed downward across two or more percentile lines on the growth chart.
- Mention if you are concerned that your baby's head looks disproportionately small compared to their body.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- Your baby's head circumference has crossed downward across two or more percentile lines on the growth chart
- You are concerned that your baby's head looks disproportionately small compared to their body
- Your baby has developmental delays or unusual neurological symptoms along with a small head
Urgent signs to report immediately
- Your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills
- Your newborn's head circumference is more than 3 standard deviations below the mean, as this warrants urgent brain imaging and evaluation
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members
Related Resources
Bottom line
Most cases of head seems too small (microcephaly) are normal. Talk to your pediatrician if your baby's head circumference suddenly stops growing or decreases, especially if accompanied by seizures, excessive irritability, feeding difficulties, or loss of previously acquired skills.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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How to Advocate for Your Child's Needs
You know your child better than anyone, and your observations matter. If you feel something is not right with your child's development or health, you have every right to ask questions, request evaluations, and seek second opinions. Advocating for your child is not being difficult - it is being a good parent.
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