Until a few years ago, most people had never heard of microcephaly, an otherwise very rare birth defect. However, due to an increase in microcephaly cases during a Zika virus outbreak that began in Brazil in late 2015, experts have confirmed that babies whose mothers contract the Zika virus during pregnancy have an increased risk of being born with microcephaly.
What parents need to keep in mind: The odds of an infant being born with this condition are still extremely rare — especially in the United States. The Centers for Disease Control and Prevention (CDC) have reported no new cases of Zika virus transmissions in the continental U.S. since 2018.[1] Here's what expecting and new parents need to know.
What is microcephaly?
Microcephaly is a very rare birth defect occurring in approximately 1 baby per every 800 to 5,000 births in the U.S.[2] Babies who are born with microcephaly have smaller-than-average head circumferences and can potentially have lifelong disabilities.
Experts measure head circumference using standard deviation, a mathematical term that basically means the difference is very significant and noticeable. So keep in mind that if your baby has a slightly small head, it doesn't mean she has a birth defect.
While no universal definition exists, some experts define mild microcephaly as the head being more than two standard deviations below average, while severe microcephaly is defined as a head size more than three standard deviations below average. But all degrees of the disorder can cause major developmental problems depending on how they impact the brain's structure.
"Primary microcephaly" has traditionally been considered to be a specific genetic mutation that causes abnormal brain development. However, in recent years, researchers have pinpointed a number of gene mutations that may cause microcephaly, which means this definition is constantly expanding.
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What causes microcephaly?
Microcephaly is most commonly caused by one of several factors:
- A genetic mutation
- Exposure to certain viruses during pregnancy, including Zika virus, rubella (German measles, which you are protected from if you received all recommended rounds of the MMR vaccine), toxoplasmosis and cytomegalovirus
- Severe maternal malnutrition or starvation during pregnancy
- Exposure to harmful substances like alcohol, drugs and toxic chemicals during pregnancy
- A brain injury after birth, usually due to lack of oxygen or certain kinds of infections
What's the link between microcephaly and the Zika virus?
A few years ago, the CDC confirmed that babies whose mothers are exposed to or infected with the Zika virus during pregnancy have an increased risk of developing microcephaly. Zika is a mosquito-borne infection similar to dengue fever that has spread throughout certain parts of Central and South America, the Caribbean, Asian and the Pacific Islands, and in Miami-Dade County, Florida. No vaccine protects against the virus.
The good news: Currently, there are no ongoing outbreaks of the virus in any country or territory.[3] The CDC still recommends that pregnant women or those trying to become pregnant take certain precautions, like talking with your health care provider before traveling abroad and taking steps to prevent mosquito bite.
How and when is microcephaly diagnosed?
Microcephaly can be diagnosed during pregnancy or after a baby is born. During pregnancy, a diagnosis comes late in the second trimester or early in the third trimester using an ultrasound. That said, it's most often diagnosed after birth, when doctors measure head size during a physical examination and compare that measurement to population standards.
When the birth defect is suspected, doctors usually order CT scans or MRIs to look closer at the baby's brain structure. A microcephaly diagnosis can come later in babies who develop the condition after birth due to a brain injury.
What conditions are associated with microcephaly?
A microcephalic baby has a head, and usually a brain, that's smaller than average. This can create structural brain problems that cause a combination of other conditions that range from mild to severe, depending on the degree of the disorder, including:
- Seizures and, potentially, epilepsy
- Feeding difficulty, including problems swallowing
- Increased movement of the arms and legs (spasticity)
- Developmental delays relating to speech, standing, sitting and walking
- Intellectual disabilities
- Hearing loss
- Vision problems
Does a baby with microcephaly have a shorter life expectancy?
There is no standard life expectancy for microcephalic babies because outcomes depend on so many factors, and the severity of the condition can vary. Babies with mild microcephaly may still meet the same milestones like speaking, sitting and walking as a child without the disorder. But in some cases, the condition can cause life-threatening problems.
What treatments are available for microcephaly?
Microcephaly is not correctable, meaning you can't increase a baby's head circumference. But early intervention with speech and occupational therapy can minimize some of the associated developmental problems. The earlier it's diagnosed, the better. Kids with microcephaly may require more frequent health care visits and counseling.
For children who have seizures as a result of the disorder, medications can be used to control episodes.
Genetic counseling is also recommended for parents who have already had a child with the disorder to examine risk factors in later pregnancies.
Resources for parents with microcephalic babies
If you have a microcephalic baby, know that you are not alone. Learning to care for a child with a birth defect like microcephaly can be emotionally and physically challenging, but talking to experts or other parents who have children with the condition can be a huge help. A few resources for parents and caregivers:
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