Health Advice: Birth Defects
Types of birth defects
There are two main types of birth defects:
- Structural defects: a particular body part is absent or improperly formed. Some examples include spina bifida, cleft palate, hypospadias and ventricular septal defect.
- Metabolic defects: one of the body’s chemicals such as an enzyme is missing or doesn’t form correctly. Some examples include phenylketonuria (PKU), galactosaemia and Tay-Sachs disease.
Causes of birth defects
Some of the factors that may cause birth defects include:
- Genetic disorders – an altered or ‘faulty’ gene or set of genes usually means that the information contained in the particular gene is either changed or missing.
- Alcohol or drugs – Some drugs are considered teratogenic. Drugs such as alcohol, tobacco, some illegal drugs and certain prescription and over-the-counter medications are known to cause birth defects if taken during pregnancy.
- Individual pregnancy factors – for example, the mother’s blood and the baby’s blood may be incompatible (Rh disease), or there could be too little amniotic fluid in the womb.
- Maternal illness during pregnancy – Some infectious diseases can cause serious harm to a pregnant woman or her unborn baby.
- Radiation exposure – from x-ray machines or other sources can damage the genes of the developing baby, particularly during the first trimester (first three months of pregnancy).
- Unknown causes – the cause of birth defects is unknown in about six in every 10 cases.
Prenatal diagnosis of birth defects
Some women may be at increased risk of having a baby with birth defects because of maternal factors such as age, general health, medical history or family history. Some of the prenatal tests used in the diagnosis of birth defects may include:
- Prenatal ultrasound scan – a non-invasive scan that uses sound waves to create a picture of the baby within the womb.
- Maternal blood tests – to check for certain substances such as hormones or particular proteins made by the baby.
- Amniocentesis – the doctor inserts a needle through the mother’s abdominal wall and takes a sample of amniotic fluid for testing.
- Chorionic villus sampling – a sample of the placenta is taken using a small needle and tube (catheter) inserted through the mother’s cervix or through her abdominal wall.
- Percutaneous umbilical blood sampling – the doctor inserts a needle through the mother’s abdominal wall into the umbilical cord. A sample of the baby’s blood is taken from the cord for testing.
Reducing the risk of birth defects
A baby may have a birth defect even when the mother and father do everything right. However, there are some precautions you can take to reduce the risk of birth defects. General suggestions include:
- Make sure you are up to date with your immunisations (especially for rubella) before you get pregnant
- Seek treatment for any sexually transmissible infection (STI) before you get pregnant
- Take folic acid supplements prior to conception and during the first trimester as directed by your doctor
- See your doctor regularly for prenatal care
- Avoid illegal drugs during pregnancy
- If you take medication to manage a chronic illness, don’t stop or alter the dose without the knowledge and consent of your doctor
- Eat a healthy diet rich in vitamin B
- Avoid unnecessary x-ray examinations
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