Traditionally, the methods used to test a mother’s growing fetus for abnormalities are highly invasive and pose a serious risk to the developing child. Due to advances in genetics in recent years, newer far less invasive procedures are now available to expecting mothers that offer equally valid, and in some cases, possibly more reliable results without the need to put the child at risk. Non-invasive prenatal screening involves taking a simple blood sample from a mother who is at least 10 weeks along in her gestation period. The blood is centrifuged to separate the blood plasma from the denser red blood cells, and what's left is a solution containing just cell-free DNA (cfDNA) fragments from both the fetus and the mother. The majority of the cfDNA will be from the mother, but for reliable results in this test, a percentage of just 4% fetal DNA is adequate. The analysis is done by looking at the proportions of fragments found from each of the child’s 23 chromosomes and looking for higher or lower than expected proportions of certain chromosomal fragments that could indicate a trisomy or chromosomal deletion. For example, finding a higher proportion of cell-free DNA (cfDNA) fragments from chromosome 21 of the fetus suggests the child is at a higher risk of being born with Down Syndrome. All this has only recently become possible thanks to advances in the speed and efficiency at which genetic sequencing can be performed. The samples of multiple patients may be sequenced at once leading to a much faster and cost-efficient way of analyzing DNA.
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