Hereditary Cancer Syndrome

Hereditary Breast Cancer

Hereditary Colon Cancer

Prenatal Genetic Counselling

Genetic Testing

Prenatal genetic counselling

Jump to Top


What is prenatal genetic counselling?

Prenatal genetic counselling helps you understand the role of prenatal testing and how it is used to interpret the risk for you to have a baby with a birth (congenital) defect or genetic condition.  Emotional support is given to help you come to terms with your risk, enabling you to make informed medical and personal decisions regarding your pregnancy.  

Jump to Top


When to consider prenatal genetic counselling?

  • If you are pregnant and over the age of 35 years - also referred to as advanced maternal age (AMA).
  • You have a child or a family history of a genetic condition, chromosome abnormality, a birth defect or developmental delay.
  • You are from an ethnic group at higher risk for a genetic condition.
  • You have a personal or family history of miscarriages or stillbirths.
  • You and your partner are close relatives or first cousins.
  • You have a medical condition that could affect your baby, such as diabetes.
  • You are taking medication that could affect your baby, such as anti-epileptics.
  • You have been exposed to substances that may cause birth defects, such as prolonged exposure to radiation.
  • You had infection(s) during your pregnancy that could affect your baby, such as rubella,chicken pox, or cytomegalovirus.
  • If you had alcohol or took recreational drugs during your pregnancy.
  • Prenatal screening test results indicated that your pregnancy is at an increased risk.
  • You are worried about your risk of having a child with a birth defect or genetic condition.

Jump to Top


What are prenatal tests?

Prenatal tests are tests performed during pregnancy to identify the chance (or risk) for your baby to be born with a birth defect (congenital) or a genetic condition.

Jump to Top


How is prenatal testing used to define risk for your pregnancy?

  • In South Africa 5% of children are born with a birth defect.
  • Everyone is at risk of having a child with a birth defect.
  • Prenatal testing is used to find out if the risk of a birth defect in your pregnancy is considerably greater than that of the average population.
  • Your overall risk for a birth defect in a pregnancy is made up of a basic risk which is changed (increased or decreased) based on identification of certain features during prenatal testing. Basic Risk + Outcome of Prenatal Testing = Overall Risk for a baby with a birth defect
  • Your age at the time of pregnancy (maternal age) is your basic risk.
  • If your overall risk is greater than the recommended risk (risk of 1 in 300 for a chromosomal abnormality and 1 in 128 for a neural tube defect) then you are said to have an increased risk or are at high risk for a baby with a birth defect
  • You will then be offered further testing and relevant support for your pregnancy.
  • Genetic counselling will help you interpret the prenatal test results and the overall risk.

Are there different types of prenatal tests?

Yes. There are two types of prenatal tests, screening and diagnostic, and they differ based on the certainty of the result.

  • Screening tests identify if you are at a increased risk of having a baby with a birth defect but the results are inconclusive
  • Diagnostic tests confirm the presence or absence of a specific birth defect or genetic condition and the result is conclusive.

Jump to Top


Summary of the differences between Prenatal Screening Tests and Prenatal Diagnostic Tests:

 

Screening Prenatal Tests

Diagnostic Prenatal Tests

Who

All pregnant women

  • Pregnancies with an increased risk for a birth defect or genetic condition.

Often identified through prenatal screening

Result

Risk for a birth defect (inconclusive)

Diagnosis of a birth defect or genetic condition (mostly conclusive)

First Trimester Tests (9 to 14 weeks gestation)

  • Maternal serum screen (9 – 13.6 weeks)
  • Ultrasound examination (10.5 – 14 weeks) measure the  nuchal translucency, detect nasal bone and assess structural development (heart, brain)
  • Chorionic villus sampling or CVS (11 to 14 weeks) detects specific chromosomal abnormalities or genetic conditions

Second Trimester (16 to 23 weeks gestation)

  • Maternal serum screen or triple screen (14 to 18 weeks)
  • Ultrasound or Fetal Anomaly scan (18 to 23 weeks) measure nuchal fold, assess development, detect major structural abnormalities and identify markers associated with genetic conditions.
  • Amniocentesis (16 to 20 weeks) detects specific chromosomal abnormalities or genetic conditions

Third Trimester (from 24 weeks)

Ultrasound (very limited)

Cordocentesis (18 weeks or later) detects specific chromosomal abnormalities or genetic conditions


Download the PDF version of this table

Jump to Top


TIMING OF PRENATAL SCREENING AND TESTING


First trimester screening (9 weeks to 14 weeks of pregnancy)

 

What is a first trimester screen?

  • The first trimester screen is a combination of an ultrasound scan and a maternal serum screening test.
  • The maternal serum screen is optimally performed between 9 and 10 weeks (extending to a maximum of 13.6 weeks) and measures the levels of two products, β-hCG and PAPP-A.
  • The ultrasound scan is optimally performed between 11 and 13.6 weeks of pregnancy and measures the nuchal translucency (NT), determines the presence of the nasal bone and assesses structural development of your baby.

What do the results from the first trimester screen mean?

  • A result from your first trimester screen test determines the risk for your baby to have a birth defect, chromosomal abnormality or genetic condition, compared to your basic age related risk.
  • If your risk is significantly greater than the age related risk then you will be offered prenatal diagnostic test, such as a chorionic villus sampling.  

What are the limitations of the first trimester screen?

  • Your first trimester screening test result does not conclude whether there is a birth defect or chromosomal abnormalities.
  • There is a risk of a false positive result.
  • An abnormal first trimester screen result may provoke anxiety.

What are the benefits of the first trimester screen?

  • The combined screen (ultrasonography and maternal serum screen) detects more than 90% of pregnancies where the baby has Down syndrome.
  • It detects a higher percentage of Down syndrome cases than the second trimester screen.
  • It allows for early detection of an increased risk for chromosome abnormalities.
  • If an increased risk is detected, an early diagnostic test (chorionic villus sampling) can be performed.
  • Early detection allows more time for counselling and decision-making in the pregnancy.
  • A negative result may allow for reassurance about the pregnancy.

Jump to Top


Second trimester screening (16 to 23 weeks of pregnancy)

What is a second trimester screening test?

  • This second trimester screening test is a combination of a maternal serum screening test and an ultrasound scan.
  • The maternal serum screening test is optimally performed between 14 and 18 weeks and measures the levels of three products (triple test); estriol, free β-hCG and alpha-fetoprotein or four (quadruple test) by including inhibin-A.
  • The ultrasound scan, also called a Fetal Anomaly Scan, is ideally performed between 18 and 23 weeks of pregnancy and is used to measure the nuchal fold, assess structural development of your baby, and detect major and minor structural markers.

What do the results from a second trimester screen mean?

  • A result from your second trimester screen test determines the risk for your baby to have a birth defect, chromosomal abnormality or genetic condition, compared to your basic age related risk.
  • If the risk is significantly greater than the age related risk then you will be offered a prenatal diagnostic test, such as an amniocentesis.  
  • The ultrasound scan can detect structural abnormalities e.g. a neural tube defect

 

What are the benefits of a second trimester screen?

  • The combined screen (ultrasound scan and maternal serum screen) detects more than 75% of pregnancies where the baby has Down syndrome.
  • A negative result may allow for reassurance about the pregnancy.

What are the limitations of a second trimester screen?

  • Your second trimester screen result does not conclude the presence of a birth defect or chromosomal abnormalities.
  • There is a risk of a false positive result.
  • An abnormal second trimester screen may provoke anxiety.
  • Diagnostic testing(amniocentesis or cordocentesis) is performed later in pregnancy and may complicate decision making for the future of the pregnancy.

Download the PDF Summary of the First and Second Trimester Screening

Jump to Top


TYPES OF PRENATAL TESTS

NON-INVASIVE TESTS


Ultrasound Scan(ultrasonography or sonar)

What is an ultrasound scan?

  • A non-invasive technique.
  • Uses sound-waves to generate a picture of your baby in the womb.
  • Used to assess the structure and development of the growing baby.
  • Both a diagnostic and screening prenatal test.

What is the difference between an abdominal and transvaginal ultrasound scan?

  • The probe for an abdominal ultrasound scan is rested on the skin of your pregnant abdomen. 
  • Transvaginal ultrasound, the probe is inserted into your vagina.

When should an ultrasound be performed?

  • Dating scan (from 4 to 5 weeks).
  • First trimester (10.5 to 14 weeks).
  • Second trimester (18 to 23 weeks).

What does an ultrasound scan detect?

  • Number of babies present.
  • Determines the gender of your baby (16 to 20 weeks).
  • Measures the size and position of your baby.
  • Listen to the heart beat of your baby.
  • Measure amount of amniotic fluid in the womb.
  • View the blood flow from the mother to the baby.
  • Identify structural and non-structural markers.
  • Structural markers (major markers):
  • These are structural abnormalities that affect function or that is present in chromosomal abnormalities or genetic conditions e.g. neural tube defect.

  • Non-structural markers (minor markers):

Features present in the baby and are associated with an increased risk for a birth defect but not conclusive and prompts further assessment.

What are some examples of structural markers viewed on ultrasound (and what they mean)?

Nuchal translucency (clear space due to accumulation of fluid at back of baby’s neck)

  • Measured from (10.5 to 14 weeks)
  • If greater than 2.5mm = increased risk

Nuchal fold 

  • Measured during second trimester
  • Greater 5mm (<20 weeks) and 6 mm (>20 weeks)=increased risk

Major structural markers:

  • Nasal bone, long bones (thigh and upper arm bones), feet, hands, skull, spine, heart.

Minor structural markers:

  • Appearance of bowel, heart and brain. 

 

What are the benefits of ultrasound?

  • The procedure is non-invasive as there is no cutting or inserting of a needle and safe for you and your baby (no risks or side-effects).
  • A normal ultrasound result can reassure you about your pregnancy.

What are the limitations of ultrasound?

  • An ultrasound scan can be affected by some of the mother’s characteristics, such as ethnicity, weight, perceived timing of conception.
  • The experience of the ultrasound scan operator.

Jump to Top


MATERNAL SERUM SCREENING

What is maternal serum screening?

  • Maternal Serum Screening is the measurement of the level of certain products (proteins) in your blood when you are pregnant.  
  • Four products are measured and these include: Papp-A, β-hCG, estriol, and alpha fetoprotein (AFP).
  • These four products are present in ALL pregnancies.
  • More or less of the normal amounts of these products during specific times in your pregnancy indicate an increased risk (or Positive) for particular birth defects and chromosomal abnormalities e.g. neural tube defect and Down syndrome, respectively.

When should a maternal serum screening test be performed?

First trimester (9 to 13.6 weeks) – optimally 9 to 10 weeks

  • Papp-A, β-hCG

Second trimester – 14 to 18 weeks

  • Triple test: β-hCG, estriol, and alpha fetoprotein (AFP)
  • Quadruple test: β-hCG, estriol, and alpha fetoprotein (AFP) and inhibin-A

What does a maternal serum screening test detect?

  • A maternal serum screen measures the amounts of specific products in your blood.
  • The result identifies if your baby is at an increased risk (positive) forchromosomal abnormalities such as trisomy 21 (Down syndrome), Trisomy 18 and Trisomy 13 and birth defects, such as neural tube defect.

What are the limitations of the maternal serum screening test?

  • The result of the screening test is affected by certain features of the mother such as ethnicity, weight, smoking and method of conception.
  • The test is known to have a 5% false positive result - meaning that in 1 in 20 women will be told that their pregnancy has an increased risk but there is no additional risk.
  • The results are not conclusive as it only detects about 65% of pregnancies with a chromosomal abnormality.  This can be improved by including the result of other screening tests such as an ultrasound scan.

 

What do the results of the maternal serum screening tests mean?

  • The result of the maternal serum screen will be given to you as a risk (positive or negative) of whether your baby may have a chromosomal abnormality or birth defect, neural tube defect.
  • This risk is used to change your basic risk (based on your age).

 

What are the advantages of maternal serum screening?

  • Non-invasive testing.
  • No risk to your pregnancy.

Download the PDF summary of Non-invasive Prenatal Tests

Jump to Top


INVASIVE PRENATAL TESTS


CHORIONIC VILLUS SAMPLING (CVS)

What is Chorionic Villus Sampling or CVS?

Chorionic villus sampling is the testing of cells from the placenta (chorionic villus cells) to detect the presence of a chromosomal abnormality and/or specific genetic conditions.

How is a chorionic villus sampling procedure done?

  • An ultrasound scan (abdominal) is used to see the position of the placenta and your baby in the womb.
  • A thin needle is inserted through your pregnant abdomen to take a sample from the placenta, using the ultrasound picture to guide the needle and avoid damage to your baby.
  • This sample is sent to a genetics laboratory to test for specific chromosomal abnormalities and/or genetic condition(s).

When should a chorionic villus sampling be performed?

  • 11 to 14 weeks gestation

What does a chorionic villus sampling test detect?

  • The results from the test will confirm whether your baby has a specific chromosomal abnormality and/or genetic condition(s).

What are the benefits of a chorionic villus sampling test?

  • The results are conclusive in determining the presence of specific chromosomal abnormalities and/or genetic condition(s).
  • An early result allows you to make future decisions in the early stages of your pregnancy.

 

What are the limitations of chorionic villus sampling?

  • Chorionic villus sampling cannot diagnose ALL birth defects.

What are the risks associated with having a chorionic villus sampling?

  • There is a miscarriage risk of less than 2%.
  • A different diagnosis may be made other than that which was suspected.

Jump to Top


AMNIOCENTESIS

What is an amniocentesis?

A sample of the amniotic fluid is taken and tested to detect the presence of a chromosomal abnormality, neural tube defect and/or a specific genetic condition.

How is an amniocentesis performed?

  • An ultrasound (abdominal) scan is used to see the position of your baby in the womb.
  • A needle is inserted through your abdomen into your womb (uterus) to take a small sample of the amniotic fluid around your baby.
  • This sample is sent to a genetics laboratory to test for specific chromosomal abnormalities and/or genetic condition(s).
  • Some of the sample is used to measure the amount of the product alpha-fetal protein (AFP) to determine the presence of a neural tube defect.

When should an amniocentesis be performed?

  • Ideally between 16 and 20 weeks gestation

What does an amniocentesis detect?

  • The results from the test will confirm whether your baby has a specific chromosomal abnormaly and specific genetic conditions.
  • Sometimes the sample will be used to measure the blood product, alpha-fetoprotein levels (AFP) and this result will confirm the presence of a open neural tube defects, such as spina bifida.

What are the benefits of amniocentesis?

  • The results are conclusive and confirm the presence of specific chromosomal abnormalities and/or genetic condition(s) and open neural tube defect.

What are the limitations of amniocentesis?

  • The amniocentesis cannot diagnose ALL birth defects only those that are being tested.

What are the risks associated with having an amniocentesis?

  • There is a miscarriage risk of less than 1%
  • A different diagnosis is made which was not suspected.

Download the PDF Summary of Invasive Prenatal Tests

Jump to Top


Undergoing Invasive Procedures

What happens during an invasive test?

  • Both chorionic villus sampling and amniocentesis are outpatient procedures.
  • On average the procedure takes 20-30 minutes (this is dependent on the specialist performing the procedure).
  • No general anaesthetic is given but a local anaesthetic may be offered.  You are awake during the procedure.
  • Feelings of discomfort, cramping or pinching may be experienced, but little or no pain.

What are you advised against after having an invasive procedure?

  • For a day or two after the procedure you should refrain from strenuous activities including heavy lifting, sex and heavy exercise.

What are some of the complications that may occur after an invasive prenatal diagnostic test?

  • Risk of miscarriage.
  • You may experience cramping or spotting after the procedure. Although common, if concerned you should contact your doctor.
  • Other complications include leakage of amniotic fluid, fever, or infection.  If any of these occur you should contact your doctor immediately.

How long after the procedure should you get your results?

  • Certain conditions (Down syndrome, trisomy 13, trisomy 18 and sex chromosome abnormalities) can be identified within three days of having a chorionic villus sampling or amniocentesis.
  • For other chromosomal abnormalities or genetic condition it can take two to three weeks for a final result.

What happens if the result of the diagnostic test shows that my baby has a birth defect, chromosomal abnormality or genetic condition?

  • You can discuss the result with your genetic counsellor.
  • You will be provided with information about the cause, long-term effect and future management of the condition. 
  • You will receive support to help you cope with the diagnosis.
  • Various options for your pregnancy will be discussed including the benefits, risks and limitations. 
  • You will be given all the information enabling you to make personal decisions and you will be supported throughout the decision-making process.

Jump to Top



 

Quick Links

Specialist Referrals

Support Groups

Resources

Events

Glossary

Testimonials

Feedback

FAQ

Disclaimer

© 2015 GC Network (Pty) Ltd