One page summary: Microcephaly after birth injury

In two sentences

Microcephaly means a head that is much smaller than expected for a baby of that age and sex. Because the skull grows in response to the brain inside it, a small head usually means the brain grew less than expected. ¹

The most important question is not the number. It is whether the head was already small at birth, or whether it started at a normal size and then fell behind. Those two situations point to different causes and different timing. ²

The numbers, with their sources

• How it is defined. A head circumference below a set cutoff on a standard growth chart for age and sex, most often more than two standard deviations below the mean ¹
• Why the skull follows the brain. A baby's skull bones are not fused, so the skull expands as the brain grows. Head circumference is therefore an inexpensive proxy for brain growth ²
• The key distinction. Microcephaly present at birth points to something during pregnancy. A head that starts normal and falls behind points to an injury or process around or after birth ²
• A common route after birth injury. Severe hypoxic-ischemic encephalopathy, where brain tissue lost after the injury results in slowed head growth over the following months ²
• What it does not settle. Head size alone does not determine intellectual outcome. Children with microcephaly range from significant disability to typical development ¹
• Measurement matters. A single measurement is far less useful than measurements plotted over time, and technique affects the number ³

What to do this week

1. Ask to see the head circumference measurements plotted over time, not just the latest number.
2. Ask whether the head was small at birth or fell behind afterward.
3. Ask whether both parents' heads have been measured.
4. Ask what genetic testing has been done and what is left.
5. Ask what the MRI showed.
6. Arrange hearing and vision assessments.
7. Refer to early intervention today.

Questions to take with you

Take these with you. Write the answers down in the moment, because you will not remember them later.

For the neurologist or geneticist

• Was the head small at birth, or did head growth slow afterward?
• What did the MRI show?
• What genetic and metabolic testing has been done, and what remains?
• Have our head sizes been measured?
• What are you watching for over the next year?

For the pediatrician

• Can I see the growth chart with all the plotted points?
• Are hearing and vision assessments arranged?
• What is the follow-up schedule?

You can also build a printable list with the question generator.

Where to read more

The full page on this condition covers how it happens, causes split into what happens even with perfect care and what is associated with gaps in care, signs by age, diagnosis, treatment, outlook, daily life and lifetime cost.

Read the full page on Microcephaly after birth injury

Related pages are listed at the bottom of it, including the events that can lead to this condition and the guides that cover therapy, school and money.