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8-minute read

Key facts

  • Microcephaly is a rare condition that happens when your brain grows abnormally.
  • There are many different causes of microcephaly.
  • If you catch Zika virus while pregnant you might pass the infection on to your unborn baby. This can cause health problems for your baby, including microcephaly.

What is microcephaly?

Microcephaly is a rare condition that happens when your brain grows abnormally. Small head size is the main symptom of the microcephaly.

Microcephaly is associated with mild to severe developmental delays and disability. It is only reported in 1 in 10,000 babies in Australia.

Your baby can be born with microcephaly, or it can develop in their first few years of life.

What are the symptoms of microcephaly?

A baby with microcephaly will have a smaller head than is expected. This is usually defined as a head circumference below the 3rd percentile. This is decided using the World Health Organization’s (WHO) growth charts.

You can read more about percentiles here, and view the WHO growth charts here.

Some children will have more severe microcephaly, and a smaller head.

Small head size is the main symptom of the microcephaly.
Small head size is the main symptom of the microcephaly.

Can microcephaly affect my baby’s health and development?

Microcephaly can affect your baby in different ways, including:

Some children with microcephaly will develop normally, with no complications.

You may have questions about how microcephaly will impact your pregnancy, and what your options are. These questions can be answered by:

You can also ask about how this might affect your child in the future.

What causes microcephaly?

There are many different causes of microcephaly, including:

Substances harmful to your baby include drugs and chemicals. Microcephaly can also be caused by alcohol consumption, and fetal alcohol spectrum disorder (FASD).

Sometimes, the cause of microcephaly is unknown.

Microcephaly and Zika virus

Zika virus is an infection that is spread by mosquitoes or sexual contact. About 4 in 5 people who have Zika have no symptoms. Those people who do get symptoms might have:

  • fever
  • rash
  • tiredness
  • aches
  • pains

Zika virus is not found in Australia. Zika virus infections in Australia are generally reported in people who have been travelling. These people have usually travelled to a country where the virus is very common, such as:

  • Central America
  • South America
  • the Pacific Islands

The Australian Department of Health recommends that you should avoid travel to a country affected by Zika if you are:

  • pregnant
  • trying to become pregnant

If you are infected with the Zika virus while pregnant, you might pass the infection on to your unborn baby. This can cause health problems for your baby, including microcephaly.

If you have any questions about microcephaly or the Zika virus, talk to your doctor.

How is microcephaly diagnosed?

Your baby can be diagnosed with microcephaly before or after birth. Your baby’s head may be smaller than usual for different reasons. If your doctor or paediatrician thinks your child has microcephaly they will do other tests, such as brain scans. These are done to rule out other conditions, such as autism.

Diagnosis before birth

During your pregnancy, you will likely have antenatal visits. At these visits, a doctor or midwife will discuss the health of both yourself and your baby. They can advise you about how to increase your chances of having a healthy baby.

At your antenatal visits, you are likely to have an ultrasound and other tests to check on your baby’s health. If there are any signs of a problem, your doctor will discuss this with you. Microcephaly can generally only be diagnosed by ultrasound in your third trimester. Before this stage, a smaller than expected head may not be obvious.

Diagnosis after birth

A diagnosis of microcephaly is made simply by measuring your baby's head. These measurements are usually taken when your baby is:

  • 6 weeks old
  • 4 months old
  • 12 months old

How is microcephaly treated?

There is no cure for microcephaly. If your child has microcephaly, they can access different services and treatments. These can help improve their health. As part of their treatment your child may see various health professionals such as:

Can microcephaly be prevented?

Microcephaly is linked to different causes. In some cases, microcephaly may be prevented by avoiding and managing these causes.

Conditions such as Down syndrome can be tested for in antenatal visits. This condition cannot be prevented. However, you can find support for you and for your child. You can speak with your doctor or visit Down Syndrome Australia for more information.

Eat healthily while pregnant and attend antenatal check-ups.

To prevent infections during pregnancy:

Furthermore, be sure to wash your hands with soap and water after:

  • using the bathroom
  • handling raw meat or eggs
  • handling unwashed vegetables
  • gardening
  • touching pets or animals
  • changing nappies

Preventing Zika virus infection

There are ways to prevent microcephaly from Zika virus infection. If you need to travel a country affected by Zika virus, you should:

  • follow recommendations on preventing mosquito bites
  • get tested for the infection when you return
  • avoid unprotected sex for 8 weeks when you return
  • avoid unprotected sex for 6 months if you or your partner are planning a pregnancy

Advice for preventing mosquito bites include:

  • cover as much of your skin as possible
  • use insect repellents according to the label
  • use mosquito nets when sleeping

How do I get more information about microcephaly?

If you have any questions about microcephaly you can call Pregnancy, Birth and Baby.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: September 2022

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Need more information?

Zika virus - Better Health Channel

Zika virus is a mosquito-borne virus. There is no cure, specific treatment or vaccine for Zika virus.

Read more on Better Health Channel website

Microcephaly: symptoms, diagnosis, support | Raising Children Network

Children with microcephaly have smaller than usual heads and brains. They often have intellectual disability. Early intervention can improve quality of life.

Read more on website

What we're doing to support healthy pregnancies | Australian Government Department of Health and Aged Care

A healthy pregnancy helps your baby grow strong. We provide support before, during and after pregnancy. This includes support for Aboriginal and Torres Strait Islander peoples, subsidised vaccination, clinical care and mental health support. We also help parents go alcohol- and smoke-free.

Read more on Australian Government Department of Health and Aged Care website

Call us and speak to a Maternal Child Health Nurse for personal advice and guidance.

Need further advice or guidance from our maternal child health nurses?

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