Port Moresby Medical Laboratories (POMMEDLAB)

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Question 1. What is Triple Test?

Approximately 2% of births are associated with congenital abnormalities of which 1 in 7 are chromosomal. The most common chromosomal abnormality is Down’s Syndrome.   Downs syndrome babies have multiple inherited defects including intellectual disability, bowel and heart abnormalities and risk of leukaemia. They suffer early dementia at age 40-50 and suffer many disabilities that are costly and mentally straining for parents and carers.

 

The risk of having baby with Downs syndrome is higher with maternal age. For example, at age 35 the risk of having Downs Syndrome baby is 1 in 400 and at age 45 is 1 in 20 compared to 1 in 1000 at age 21 years.

 

Hence, the Triple Test a blood test used as a primary screening tool to assess the chance of the pregnancy being affected by Down’s syndrome. The results from all of the biochemical tests are used together to estimate the possibility of a Down’s syndrome affected baby.

 

Question 2. What are the tests for Triple Testing?

Maternal blood is taken for measurement of AFP, b-HCG, and unconjugated oestriol. In some centres, pregnancy associated plasma Protein (PAPPA) and inhibin A are also measured. A simple routine blood sample is all that is need for Triple Test.

 

Question 3. Who should have Triple Test?

Any mother who is pregnant can request Triple Test but is strongly recommended for mothers who fall pregnant after 35 years of age or has strong family history of Downs Syndrome or any chromosomal abnormalities.

 

Question 4. When is it requested?

The screening tests may be performed as early as 9 or 10 weeks of pregnancy in some centres or around 16 weeks in others. Screening can be performed up until about 21 weeks of pregnancy.

 

Question 5. What does the test result mean?

B-HCG–                                        Increased in Downs syndrome

AFP–                                            Decreased in Downs Syndrome, increased in anencephaly (see maternal AFP)

Unconjugated oestriol–             Decreased in Downs Syndrome

 

 In reality, due to large variation in Triple Test results due to influence from many factors, biochemical risk is calculated and adjusted for  maternal age and weight to calculate the chance of the baby being affected by Down’s syndrome, or another chromosomal abnormality such as Edward’s syndrome. Additional information about family origin and smoking history may be included in the calculation to improve its efficiency. If the chance is greater than a certain cut-off value, further tests may be offered.

 

The interpretation should therefore be left to midwife or doctor familiar with Triple Test. They will be able to explain the meaning of the result and offer the choices available to the mother. If the result appears to be in the ‘higher risk’ category, more definitive tests are needed to confirm a diagnosis (See below).  When combined with 11-13th week (first trimester) ultrasound  measurement of nuchal translucency, the chance of picking up abnormality is much higher than either Triple Test or ultrasound alone.

Question 6. Is there anything else I should know?

It is important to remember that the tests described here are screening tests and not all Down’s syndrome affected pregnancies will give results in the ‘higher risk’ category. The screening results are a guide to those women who might benefit from further more invasive tests. It is important to stress that only a small proportion of women who are in the ‘higher risk’ category for Down’s syndrome by Triple Test will have an affected baby.

 

The screening results are very dependant on an accurate age for the baby and this is why a dating ultrasound scan (preferable between 7-10 weeks ) is recommended prior to screening. If the gestational age of the baby is not correct, the screening result may be falsely high or low. An early ultrasound scan will show the possibility of twins or triplets and these will result in high maternal AFP levels.

 Question 7. What is the definitive test?

The definitive test for Down’s syndrome is an amniocentesis (10-13 weeks) or chorionic villus (6-7weeks) sampling procedure .A small amount of fluid surrounding the baby, or a small piece of the developing placenta, is taken using a very fine needle. It is then possible to use laboratory techniques on one of these samples to look at the chromosomes of the baby and detect possible problems. There is a small risk of infection or miscarriage associated with these invasive procedures and therefore careful consideration should be given before having them performed.

 

Question 8. What are the other problems Triple Testing can identify?

Antenatal Triple Test Screening can also detect variety of other abnormalities including neural tube defects as anencephaly (baby with no brain).

A raised level of AFP by itself might indicate the possibility of a neural tube defect. A baby with an open neural tube defect has an opening in the spine, head or abdominal wall that allows higher than usual amounts of AFP to pass into the mother’s blood. See details on Maternal AFP screen.

 

Question 9. What are the risks of Triple Testing?

There is virtually no risk to you or your baby from this test.

 

Question 9. What are the benefits?

 

Most often, the test reassures you that your baby probably does not have a serious defect.

Abnormal results can help you and your healthcare provider manage your pregnancy better. Your provider may plan your delivery in a center equipped to deal with these abnormality, which may improve the outlook for your baby. Your provider can offer you counselling to help you prepare for the baby's problems. There are also many support groups for families who have children with birth defects. You may find it helpful to get in touch with these groups before or after your baby is born.

Triple Test– Down’s Syndrome Screen