Genetics and Counselling
It is generally known that 2-3% of pregnancies could be affected by a birth defect. Birth defects can have many causes, including chromosome or genetic abnormalities. We usually have 46 chromosomes, 23 pairs, in the cells that make our bodies. We inherit one of each pair from our mother, the other one from our father.
Chromosomes carry thousands of genes. Genes determine how a baby develops, looks and how the body functions. Having extra or missing chromosome material or a change in an important gene can interfere with a baby’s development. Many of these conditions happen out of the blue around conception. Sometimes, conditions can be inherited.
At your appointment, we will ask you questions about your families to estimate the chance of an inherited condition that could occur in this pregnancy.
It is now possible to test for chromosome problems and some genetic conditions prenatally. The geneticist / genetic counsellor after counselling will offer the appropriate tests.
The genetic tests can either be a screening test or a diagnostic test. Screening tests provide information about the risk of the fetus developing an underlying chromosomal abnormality while the diagnostic tests will provide results if the fetus is affected with a particular chromosomal or genetic abnormality.
Karyotype: this test is generally performed to count the number of chromosomes, for example to confirm a diagnosis of Down Syndrome, or to look for chromosome rearrangements (translocations).
Array is a chromosome test that is around 40-50 times more sensitive than karyotype. Array is usually offered when an ultrasound scan has shown a structural problem with one of the baby’s organs.
Whole exome sequencing (WES): This is a very new method of looking at individual genes. As we have over 20,000 genes with many variations between people, exome sequencing can be difficult to interpret. WES is only recommended when there are scan abnormalities.
It is important to recognise that the available tests are not able to rule out all causes of birth defects. We will discuss the best testing for your situation with you at the consultation.
