> Prenatal testing non-invasive: many false positives

The DNA test on maternal blood può give false positives. The presence of a duplication of the maternal (activitiesà of cell division) può simulate a trisomy fetal in the DNA testing Screen.

The noninvasive test that looks for the cells of fetal DNA in the mother’s blood is becoming more and more common. Two studies published online on 1 April in the New England Journal of Medicine highlight the risk of false positives, especially in women at low risk.

In one study, coordinated by Matthew Snyder, of the laboratory of Jay Shendure, of the Università of Washington, Seattle, the authors reveal the motivation of the false positives in two pregnancies.

The researchers note that the low overall rate of aneuplodia in the population to low-risk limits the predittività is a positive test. Because of this predittività positive limited, another research team, led by Sau W. Cheung, Baylor College of Medicine in Houston, Texas, argues that the procedure should be clearly described as a screening, to emphasize the needà of the confirmation test for the search of the anomalies found by the test.

The NIPT (Non-Invasive Prenatal Testing) è been used since 2011 to identify the high-risk pregnancies for aneuploidy, fetal, and many firms currently offer the test. How già reported by Medscape Medical News, the communityà scientific è recently been interested in the evaluation of the use of the test in the population at low risk.

The duplication of the maternal increases false positives

To better understand the cause of the false positives, Snyder and colleagues have examined four pregnancies.

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researchers have found that the duplication is maternal was responsible for false positives in two of the three cases of the assumed trisomy 18. The authors have not identified the reasons for the remaining two false positives.

In the second part of the study, the investigators have investigated the as the amounts and categories of duplication may influence these false positives. On the basis of these data and other studies, in most european countries, the presence of false positives seems to be very high.

These studies underline the needà to perform theamniocentesis to confirm and contrast with the results described as very accurate.

They note that they have heard of cases of anecdotes of women who have aborted the pregnancy for a test that is later revealed to be a false positive.

As recommended by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, the positive results of the screening, prenatal non-invasive must be followed by invasive diagnosis before decisions are made irreversible.

False positives in the context

The problem of false positives is particularly relevant in the population at low risk, explains Snyder, “a test for a disease with a prevalence of high, a small number of false positives is a drop in the bucket. But for a situation such as a prenatal screening in a population at low risk, the assessment of the predittività positive impacts even with a low number of positive tests.


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Source: Medscape

25 aprile 2015