What is a birth defect and what are common birth defects?

Perhaps you can relate to that pang of worry that hits when you go in for a pregnancy ultrasound or routine prenatal checkup. “I hope everything’s OK in there…” Even when you’re 99.9 per cent certain that your baby is fine, you can’t stop yourself from anxiously trying to read the doctor’s facial expressions. Or even giving telepathy a solid go. 

Your worry is not totally unfounded. ‘Birth defects’ are a major cause of death, hospitalisation, and disability in children.

Oh what a cheery piece of news—thanks Mumli.

Er, yes. Sorry. 

While no one wants to face the reality of there being something wrong with their baby, it’s worth knowing what to expect if a birth defect is diagnosed during your pregnancy. It’ll probably be stressful and upsetting AF at first, but a birth defect doesn’t necessarily mean that your child is in danger, or will have a poor quality of life. Some issues can successfully be treated with surgery, medications, or physical therapy.

And no matter what sort of birth defect your baby is diagnosed with, it’s good to know that there’s help available to you and your family—be it genetic counselling, or support for raising a child with special needs

So to start off with, let’s explore the chances of your baby having a birth defect.

How common are birth defects?

As many as 4,500 Australian babies are born each year with some form of birth defect. That’s 1.7 per cent of all births! These anomalies are often picked up during prenatal testing, but some birth defects aren’t discovered until infancy or childhood.

It sounds like a lot, but remember—not all birth defects are life-threatening.

What exactly IS a birth defect?

It’s what it’s called when any abnormality occurs in a baby’s development during pregnancy. It can also be referred to as a ‘congenital anomaly’, a ‘congenital malformation’, a ‘congenital disorder’, or a ‘congenital abnormality’. 

There are major defects and minor defects. Some might cause significant disability and require medical intervention, but others are barely noticeable and won’t affect a person’s life much. They might even go through life not knowing they live with an abnormality!

There are two types of birth defects to be aware of:

  • Structural – to do with how the body is formed, for example, a limb not fully developing.

  • Functional – to do with how the body works, for example in haemophilia the body lacks the ability to clot blood.

What causes birth defects?

That’s not always clear. Common causes of birth defects may include:

Genetic factors 

When a baby’s genetic makeup is abnormal, it may develop into genetic disorders such as Down Syndrome or cystic fibrosis. Genes may play a role in passing on some conditions like diabetes or hypothyroidism as well.

Socio-demographic factors 

The World Health Organization notes that 94 per cent of severe birth defects occur in low and middle-income countries. This may be related to a lack of access to nutrition and medical care in some cases, but there’s also a clear correlation between congenital abnormalities and maternal age (with pregnancy after 35 posing a higher risk of birth defects), and some ethnic groups have higher incidences of particular abnormalities at birth.

Environmental factors 

A mother’s exposure to some pesticides and chemicals can increase the risk of birth defects developing in pregnancy. That’s why certain jobs aren’t safe to do while you’re pregnant.

Other environmental factors can include viruses the mother contracts, or even physical restrictions in the womb if you’re carrying multiples.

Maternal health factors 

Smoking, drinking alcohol, taking drugs and certain medications, obesity, some health conditions, infections, and even what you eat can all affect the chances of a birth defect occurring. 

F*ck, there’s a lot of pressure on us mums to take care of ourselves! Try to remember that there’s only so much you can control. 

How are birth defects diagnosed?

If you’re at risk of having a baby with a birth defect (well, we all are, but say you have a family history of genetic disorders, or you’re over 35), there are a range of tests you can do before and during pregnancy, as well as routine screenings that are done on your baby after birth, to pick up any anomalies. 

Pre-pregnancy screening for birth defects

  • Genetic carrier screeningThis is a blood test that parents can take prior to conceiving. It tests for any genetic abnormalities that could pass onto your children. It doesn’t provide definitive answers, but more of a ‘chance of’ your baby developing something.

  • Embryo testing – If you’re going through IVF, you can have embryos tested for genetic complications before they’re implanted.

First trimester tests for birth defects

As most of your baby’s organs and limbs develop in the first trimester of pregnancy, some key birth defects can be picked up early on. Around weeks 11 to 13, you’ll have a maternal screening test to look for potential anomalies.

  • Blood screeningThis will measure for two types of proteins in your blood that can indicate a chromosomal disorder in your baby.

  • Ultrasound – You’ll also have a first trimester ultrasound to look for any structural defects, and assess for excess fluid which could indicate a chromosomal disorder or heart defect.

If anything looks off, or if you have other risk factors for birth defects, you might also be offered a diagnostic test in your first trimester:

  • Chorionic Villus Sampling (CVS) – This is where a doctor collects a tiny sample of your placenta and runs tests for genetic disorders. It’s usually done around weeks 10 to 12.

Second trimester tests for birth defects

In your second trimester, with your baby a bit more developed but still small enough to assess on an ultrasound, you’ll have a comprehensive anomaly ultrasound, as well as another blood test and possibly a test that checks for heart defects. These will generally be done between weeks 15 and 20.

  • Maternal Serum Screening – This blood test, sometimes called the ‘quad test’, checks for four proteins in your blood that can indicate chromosomal issues.

  • Anomaly Ultrasound – Usually done around weeks 18 to 20, this checks the size of your baby and looks for any abnormalities in their development.

  • Foetal Echocardiogram – This test uses soundwaves to check for heart defects, and can provide a more detailed image of your baby’s heart than a regular pregnancy ultrasound.

You might also be offered two more tests in your second trimester to assess for birth defects:

  • Amniocentesis – This is when your doctor takes a small sample of amniotic fluid to test.

  • High Resolution Ultrasound – This more advanced type of ultrasound can be used to pick up birth defects that don’t show up on a normal ultrasound. It may be performed around weeks 18 to 20 if your other tests indicated potential problems.

Newborn screening for birth defects

This is the norm in countries like Australia, and is often called a ‘heel prick test’. A tiny drop of your baby’s blood will be taken for analysis between 48 and 72 hours after birth, and some conditions like hypothyroidism or cystic fibrosis can be detected straight away.

Developmental tracking checkups

Some sneaky birth defects aren’t evident in newborns, but are picked up later on in life. That’s why your child health nurse likes to see your baby regularly throughout the first few years of their life. They’ll monitor your child’s growth and development milestones to help identify anything out of the ordinary.

What are the most common birth defects?

Birth defects can be as unique as each baby, and come in different stages of severity. Some of the most common birth defects include:

  • Facial malformation – including an abnormal shape of head, eyes, ears, mouth, or face. A key example of this is a cleft lip, when a baby’s mouth has a distinct hole in it which can cause trouble with feeding and breathing.

  • Limb defects – including an abnormal shape of hands, feet, or limbs, or when limbs are missing altogether. A common one is ‘clubfoot’, where a baby is born with feet turning inwards rather than pointing straight.

  • Heart problems – including structural issues that affect how the heart works, or how blood flows to other areas of the body.

  • Neural tube defects – such as spina bifida, in which the spinal cord is not fully enclosed.

The Centers for Disease Control and Prevention has an extensive list of common birth defects, which is worth looking at if you’d like in-depth information about each.

What are the treatment options for birth defects?

Treatment for birth defects will depend on what the problem is, and how severe it is. Your doctor will talk you through your options and what is recommended for your baby.


In some cases, surgery can help resolve the issue. One example is the birth defect ‘hypospadias’, which is when a male baby is born with his urethra underneath his penis rather than at the tip. Yeah—that can happen! It’s actually pretty common, with one in 200 babies in the US being affected by it.

Surgery may also be advised for facial or limb malformations, and congenital heart defects.


Sometimes medicine is prescribed to help with a birth defect. For example, some medications can assist blood flow in babies with heart defects.

Physical therapy

Some musculoskeletal defects, such as clubfoot, can be improved through gentle stretching and exercises. In more extreme cases, braces or surgery might be needed as well.

Ongoing care

Some birth defects can’t be treated or ‘fixed’, but can be well managed with ongoing care. And love. Lots of love always helps. 

Take Down Syndrome, for example. Kids with Down Syndrome can lead happy, healthy lives regardless of the condition! Some will benefit from support services like speech therapy and learning assistance.

What can you do to prevent birth defects from happening?

Let’s be clear: You can’t always stop birth defects from occurring. Sometimes they’re completely random and happen for no good reason. But research has shown that doing certain things before and during your pregnancy can reduce the likelihood of certain birth defects occurring.

Here are some things you can do:

  • Take folic acid supplements – This has been shown to significantly reduce the occurrence of neural tube defects like spina bifida. 

  • Take your prenatal vitamins Getting the right levels of nutrients into your body can improve birth outcomes and the health of you and your baby.

  • Get all your recommended immunisations – Birth defects were once far more often caused by everyday infections and diseases. Thank god for modern medicine! These are now largely preventable by getting immunised. Ask your doctor what you need to be protected from.

  • Try to avoid alcohol, drugs and smoking – Some birth defects are directly caused by these (i.e. foetal alcohol syndrome). Secondhand smoke counts, too, so force your partner to quit, and don’t walk behind smokers on the street. Avoid smokers like the plague.

  • Get OTT with your medical condition treatment – Pregnancy is the best time to take extra good care of any conditions, such as diabetes. It might be a lot of work, but it’s SO worth it. Lean on your medical team for support, and find yourself a Facebook group for pregnant people with your condition for a good morale boost too!

  • Speak to your doctor – Run any medications past them (including those woo woo herbal concoctions you may take), as some are unsuitable for pregnancy. Get advice specific to your pregnancy, and discuss any conditions, including past STIs. (Awks, but necessary.)

One final note on the matter: We’re not big fans of the term ‘birth defect’, actually. It sort of implies that your pregnancy—or your baby—are ‘defective’. That’s not the case. Your baby is perfect however they come. And they’re all yours.

Read next: Where to find help: Guide for parents with a special needs child

BetterHealth Channel, Birth defects explained

World Health Organization, Birth defects

Centers for Disease Control and Prevention, Diagnosis of Birth Defects

KidsHealth, Birth Defects (for Parents)

The Australian Birth Defects Society, What are Birth Defects?

Integris Health, What are the Most Common Birth Defects?

Peter Farlie, Developmental Biologist, Murdoch Children’s Research Institute (The Conversation), Why don’t we know what causes most birth defects?

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