Technique Detects Down Syndrome in Fetuses in Two Hours

A new technique enables pregnant women to know whether their fetus has Down syndrome in just a few hours.

Called FlashFISH, the new technique is a modification of the existing standard fluorescence in situ hybridization (FISH) test, which provides results in 24-48 hours. Another procedure, called karyotyping, delivers results between eight and 21 days.

Both FlashFISH and the standard FISH involve inserting a needle through the pregnant woman's abdominal wall to draw amniotic fluid from the womb. The amniotic fluid comes from the membranous sac, which surrounds the embryo and contains genetic material from the fetus. The FlashFISH test requires only two ml of fluid compared with 5 ml needed for standard tests. Clinicians examine fetal cells in the fluid by maneuvering a molecular probe directly into the cells' nucleus. The probe is a tiny portion of DNA that can attach to a matching sequence in the fetal cell and identify whether it is abnormal.

The new procedure was developed by assistant Prof. Mahesh Choolani, from the department of obstetrics and gynecology, National University of Singapore (NUS; Singapore), and his laboratory team. Dr Choolani reported that FlashFISH matches the accuracy of the currently used standard FISH test. He added that it poses no additional risks to the mother and costs roughly the same amount as the currently used test.

Prof. Choolani said that the test has proved to be 99% accurate in detecting Down syndrome. The new technique carries the same risk of miscarriage--about one in 100--as the traditional tests because it involves inserting a needle into the womb.

The test particularly will be useful for women who become pregnant after age 35 because they are more at risk for having a child with Down syndrome. Prof. Choolani said that they had decided to develop a faster test because, Waiting for test results can cause a lot of anxiety in couples.


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