Sequential genomic testing in prenatal diagnosis: incremental yield of chromosomal microarray and exome sequencing, real-world NIPT confirmation rates and pregnancy outcomes in 120 consecutive amniocenteses from northeastern Türkiye — a retrospective cohort study
This retrospective cohort study of 120 amniocenteses at a regional center in northeastern Türkiye demonstrates that a sequential prenatal testing pathway incorporating chromosomal microarray and exome sequencing significantly increases diagnostic yield beyond conventional cytogenetics, while highlighting critical limitations in NIPT accuracy for non-common aneuploidies and the poor prognostic implications of normal genetic results in structurally abnormal fetuses.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When a pregnancy shows signs of trouble, whether through an ultrasound scan or a blood test, parents face a narrow window to understand what is happening inside the womb. For decades, the standard way to look at a baby's genetic blueprint was to examine the chromosomes under a microscope, a process that could spot large errors like missing or extra whole chromosomes. However, science has moved forward, offering tools that can read the genetic code with much finer detail. One such tool is a chromosomal microarray, which acts like a high-resolution scanner to find tiny missing or extra pieces of DNA that a microscope would miss. Another is exome sequencing, which reads the specific parts of the DNA that tell the body how to build proteins, looking for single-letter typos that cause disease. The question for doctors and families is no longer just whether these advanced tools exist, but how much they actually help when used in real-world clinics, especially in regions where resources might be more limited than in major research hubs.
A team of researchers in northeastern Turkey set out to answer this by looking at 120 consecutive pregnancies where an amniocentesis was performed. An amniocentesis is a procedure where a small amount of fluid is taken from the sac surrounding the baby to test for genetic conditions. The study, conducted at a regional university hospital, followed a step-by-step approach. First, they used standard tests to check for common chromosome problems. Then, they added the microarray scan. Finally, for some cases where the earlier tests were normal but the baby still showed physical problems, they used the more detailed sequencing to look for specific gene errors. The goal was to see how much extra information these later steps provided and whether the results matched what parents were told before the invasive tests.
The researchers found that in 30 percent of the pregnancies, something unusual was discovered in the genetic material. Of these, about 22.5 percent were findings that would directly cause disease in the baby, while the remaining 7.5 percent were findings that meant the baby was a carrier of a condition but would not be sick themselves. Crucially, the study showed that if the doctors had stopped after the standard chromosome tests, they would have missed nearly one-quarter of the disease-causing diagnoses. The advanced microarray and sequencing tests found seven specific cases of genetic disease that the older methods could not see. These included tiny deletions or duplications of DNA and single-gene disorders. This suggests that even in a regional center with a moderate number of patients, adding these advanced layers of testing provides vital information that would otherwise be lost.
The study also looked at how reliable the non-invasive prenatal tests, which are done on a mother's blood, really are when they come back with a high-risk result. In this group of 14 families who were referred after a high-risk blood test, the results were very clear but depended entirely on what the test was looking for. If the blood test flagged a risk for the two most common chromosome problems, trisomy 21 and trisomy 18, the invasive amniocentesis confirmed the diagnosis every single time. However, when the blood test flagged risks for rarer chromosome issues or specific missing pieces of DNA, the invasive test showed that the risk was not real in most cases. In fact, for sex chromosome issues and rare chromosome errors, none of the high-risk blood test results were confirmed. This finding offers a clear message for counseling: a high-risk result on a blood test is not a final diagnosis, and especially for rare conditions, it should not be used to make irreversible decisions without a confirmatory invasive test.
Perhaps the most striking and somber finding concerned the outcome of the pregnancies. Among the families who had a documented result, the majority of decisions to end a pregnancy happened even when the genetic tests came back completely normal. In 14 of the 19 pregnancies that were terminated, the genetic workup showed no errors at all. These were cases where the baby had severe physical abnormalities seen on ultrasound, but the genetic code itself was clean. This highlights a difficult reality for parents and doctors: a normal genetic result does not guarantee a healthy baby, nor does it mean the physical problems will be mild. The genetic test can rule out specific genetic diseases, but it cannot predict the outcome of structural problems that have other causes.
The researchers concluded that a step-by-step testing pathway is feasible and highly valuable in regional medical centers. It ensures that families receive a complete picture, catching genetic diseases that older methods miss and providing clarity on the reliability of blood screening results. The study emphasizes that while technology has advanced, the interpretation of results requires care. A high-risk blood test needs confirmation, and a normal genetic test in a baby with physical problems is not a reason for false reassurance. By separating the findings that cause disease from those that are merely incidental, the doctors can give parents the most honest and accurate information possible during a time of great uncertainty.
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