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False negatives & false positives

In most cases, the diagnostic test results are correct. However, for all scientific and medical tests there is a small risk of an abnormal result when there is not really an abnormality (called a “false positive”). There is also a small risk of getting a normal result when there is really an abnormality ( a “false negative”). From published studies we know that the chance of a false result is very low.

FISH <1-in-10,000 Cytogenetic analysis <1-in-4,000
1st Trimester Screening false +ve 5%
(combined testing) false –ve 10%
Molecular testing <1%
Reference: Sydney Genetics


Fast FISH stands for fluorescent in-situ hybridisation. See Fluorescent in-situ hybridisation.

Fetal alcohol syndrome

Fetal alcohol syndrome is a rare condition which occurs when the mother ingests excessive alcohol over a long period of time in pregnancy. The baby may have intellectual disability, abnormal facial features and other problems.

This syndrome cannot be cured or treated but it can be prevented by avoiding excessive alcohol during pregnancy.


FISH stands for fluorescent in-situ hybridisation. See Fluorescent in-situ hybridisation

Fluorescent in-situ hybridisation

Fluorescent in-situ hybridisation is a laboratory technique where fluorescent labels highlight certain chromosomes and show up how many copies of that chromosome are in each cell. FISH is commonly used to analyse chromosomes number 13, 18 21 X & Y. because these are the most common chromosomes causing fetal abnormalities. These chromosomes account for 85% of abnormalities associated with advanced maternal age, high risk nuchal screening and a positive triple test. The amnio or CVS cells do not need to be grown before FISH testing so it can give results in 1 or 2 days. The full karyotype gives a more thorough examination of all 46 chromosomes and that test is usually available in 10-14 days.

Folic acid

Folic acid is a B group vitamin which has been shown to reduce the risk of Spina bifida in the baby. It is recommended that you take 0.5mg per day from one month before conception to the end of the first trimester.

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