Birth defects

A birth defect is a problem that is present at birth and happens when a baby is developing in their mother’s body. Most birth defects happen in the first 3 months of pregnancy because that is when the organs are developing.

A birth defect may affect the way the body looks, works or both. Some birth defects (such as cleft lip) are easy to see, but others (such as heart defects or hearing loss) are found using special tests. Birth defects can vary from mild to severe.

If your baby is born with a birth defect or other health condition, they may need special care at birth and later in life. You will be able to talk to your baby’s healthcare team about any questions or concerns you have.

A child born with a birth defect can still lead a normal and healthy life. Although these children may have challenges that other people don’t have, they can still do everything most other people do.

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Key points

  • Birth defects affect approximately 4.5% of all babies born in New Zealand; this rate is similar to other developed countries. 
  • Some birth defects may be found during prenatal tests, while others are not found until after the baby is born.
  • Risk factors for birth defects include a lack of folic acid, drinking alcohol immediately before or while you are pregnant, smoking cigarettes, using drugs or taking certain medications during pregnancy, as well as some types of infection, obesity and uncontrolled diabetes.
  • Not all birth defects can be prevented, but there are some things you can do to increase your chances of having a healthy baby.
  • These include planning ahead and taking folic acid daily, avoiding harmful substances, choosing a healthy lifestyle and talking to your healthcare provider about medications and vaccinations.
  • Babies with birth defects often need special care and treatments. The treatments may include surgery, medicines, assistive devices and therapies.

Types of birth defects

Researchers have identified thousands of different birth defects, but some are much more common than others. There are two main categories of birth defects: structural (how the body is formed) and functional (how the body works). In some cases, birth defects are caused by a combination of factors, leading to both structural and functional problems.

Structural birth defects

Structural birth defects relate to problems with how part of the body is formed. Some of the more common or serious problems include: 

  • cleft lip or cleft palate
  • heart defects, such as missing or misshaped valves
  • abnormal limbs, such as a clubfoot
  • neural tube defects, such as spina bifida, anencephaly or other problems related to the growth and development of the brain and spinal cord.

Functional birth defects

Functional, or developmental, birth defects are related to a problem with how a body part or body system works. They can lead to intellectual and developmental disability and can include:

What causes birth defects?

For most birth defects, the cause is unknown, but it may be due to one of the following causes:

  • Genetics – one or more genes might have a change or mutation that results in them not working properly, as in cystic fibrosis.
  • Chromosomal problems – a chromosome or part of a chromosome might be missing or there may be an extra chromosome, as in Down syndrome.
  • Not getting enough of certain nutrients. For example, not getting enough folic acid before and during pregnancy is a key factor in causing neural tube defects.
  • Exposure to harmful substances such as alcohol, cigarettes or certain medicines.
  • Infections during pregnancy, such as rubella.

How are birth defects identified and treated?

Some birth defects can be diagnosed during pregnancy with prenatal tests. Others are not found until after the baby is born. Sometimes the defect is obvious right away, while other times it may not be discovered until a problem develops. Most birth defects are found within the first year of life.

Treatment will depend on the symptoms and problems caused by the particular birth defect. Treatments range from medications to therapies, surgeries and assistive devices.

How can birth defects be prevented?

Not all birth defects can be prevented. However, you can increase your chances of having a healthy baby by adopting a healthy lifestyle and managing health conditions before you become pregnant.

The following factors increase your risk of having a baby with a birth defect: lack of folic acid, drinking alcohol immediately before and while you are pregnant, smoking cigarettes, using drugs and taking certain medications during pregnancy, as well as some types of infection, obesity and uncontrolled diabetes.

If you are planning to become pregnant, make a PACT with yourself to take the following actions:

  • Plan ahead and take 800mcg of folic acid every day. This can help prevent major birth defects of the developing brain and spine.
  • Avoid harmful substances, including alcohol, cigarettes and other drugs, and food-borne bugs. These can all cause complications in pregnancy and birth defects. See alcohol and pregnancy and smoking and pregnancy.
  • Choose a healthy lifestyle – try to achieve and maintain a healthy weight and keep diabetes under control. Obesity and poor diabetes control increases the chance of birth defects and other problems in pregnancy. See eating, drinking and watching your weight in pregnancy and pre-existing diabetes and pregnancy.
  • Talk with your healthcare provider about any medications you are taking and any vaccinations you may need. Certain medications can cause serious birth defects if they are taken during pregnancy. Most vaccinations are safe during pregnancy and some vaccinations, such as the flu vaccine, are specifically recommended during pregnancy. See pregnancy and immunisation.

Learn more

Pregnancy is an exciting time, but it also can be stressful. Knowing that you are doing all that you can to get ready for pregnancy, staying healthy during pregnancy and giving your baby a healthy start in life will help you to have peace of mind. For more information, see our pregnancy section.

Pregnancy and newborn screening National Screening Unit
Birth defects and other health conditions March of Dimes, US
Specific birth defects Centers for Disease Control and Prevention, US, 2017


  1. Birth Defects Medline Plus
  2. Facts about birth defects CDC
  3. Birth defects National Institute of Child Health and Development, US
  4. New Zealand birth defects registry NZBDR, 2014

Reviewed by

Dr Jeremy Tuohy is an Obstetrician and Gynaecologist with a special interest in Maternal and Fetal Medicine. Jeremy has been a lecturer at the University of Otago, Clinical leader of Ultrasound and Maternal and Fetal Medicine at Capital and Coast DHB, and has practiced as a private obstetrician. He is currently completing his PhD in Obstetric Medicine at the Liggins Institute, University of Auckland.
Credits: Health Navigator Editorial Team. Reviewed By: Dr. Jeremy Tuohy, Researcher & Clinician, University of Auckland Last reviewed: 08 Nov 2017