Download Amniocentesis and CVS: QF-PCR analysis. Information for Parents

Amniocentesis and CVS: QF-PCR analysis. Information for Parents
QF-PCR analysis
QF-PCR analysis is performed on the cells collected at CVS or amniocentesis. It is a test which can inform
parents if their baby has Down’s syndrome (trisomy 21), Edwards’ Syndrome (trisomy 18), Patau’s Syndrome
(Trisomy 13) and some abnormalities of the sex chromosomes.
Why has QF-PCR been offered to me?
The screening test that you have had in pregnancy shows that your baby has an increased risk of either
Down’s Syndrome, Patau’s Syndrome or Edwards’ Syndrome. QF-PCR analysis can be used to find out if the
baby has one of these chromosome problems.
What are chromosomes?
Chromosomes are the structures in the centre of each cell in the body that contain our genetic information or
genes. Genes are instructions which tell the body how to develop and function. Each cell has 46
chromosomes in 23 pairs. We inherit one of each chromosome from each parent to make a pair. The pairs
are numbered from 1 to 22 from the largest to the smallest. The 23rd pair are the sex chromosomes X and Y.
Usually girls have two X chromosomes (46, XX) and boys have one X and one Y chromosome (46, XY).
Testing chromosomes
In the past chromosomes have been looked at with a microscope to detect visible changes in them. This
picture of the chromosomes is called a karyotype. The QF-PCR test is different because it does not look at a
picture of the baby’s chromosomes, instead it counts those which are most likely to occur in abnormal
number. The QF-PCR test will detect if there is an extra chromosome 21 (called Down’s syndrome or trisomy
21), an extra chromosome 18 (Edwards’ syndrome, trisomy 18) or an extra chromosome 13 (Patau
syndrome, trisomy 13). QF-PCR will also identify if a baby has extra or missing X and Y chromosomes.
What are the advantages of QF-PCR?
▪ QF-PCR can count the chromosomes mentioned above very accurately and rapidly.
What are the limitations of QF-PCR?
▪ QF-PCR does not count or visualise any other chromosomes apart from 21, 18, 13, X and Y, so it will not
detect other chromosome abnormalities or alterations in single genes. Many genetic conditions are not
caused by whole chromosome problems but result from very tiny changes in individual genes and these are
not covered by this test.
▪ In the UK there is wide experience of looking at QF-PCR results alongside the karyotype when the
screening test shows an increased risk. Reports in the medical literature show that if the mother has a normal
ultrasound scan and normal QF-PCR test, the residual risk of the baby having a significant chromosome
abnormality that would have been detected by the karyotype is less than 0.5% (or 1:200).
▪ Very rarely the QF-PCR test fails to give us a result when the options will be discussed with you.
How will I be given the result?
The result will usually be available in 3 -5 working days after the procedure and a Specialist Midwife in the
Fetal Medicine Unit will contact you. If the QF-PCR result is abnormal it will be discussed with you including
the option of further tests.
Further questions
If you have further questions about this test, please contact the Specialist Midwife in the Fetal Medicine Unit
on 0117 342 5470
University Hospitals Bristol Healthcare NHS Foundation Trust
0117 342 0000 Minicom 0117 94 9869 www.UHBristol.nhs.co.uk
Page 1 of 1