Womb test for mongol babies

Press, 19 June 1979, Page 19

Womb test for mongol babies

Scientists have taken the first step towards the development of a simple blood test to screen women early in pregnancy for genetic abnormalities such as mongolism in their babies. The test involves the examination of cells from the baby which pass into the mother’s bloodstream. Dr Leonard Herzenberg and his colleagues at Stanford University School of Medicine in California, where the work is being carried out, says: “We have for the first time shown that as early as 15 weeks into pregnancy small numbers of foetal cells are present in the mother’s bloodstream.”

This idea had been suggested previously but not proved conclusively nor widely accepted. A successful test could have enormous social and public health impact. At present there is no practical test for screening women under the age of 35 for Downs-syndrome (mongolism) in their babies. Although babies bom to older women appear most at risk of the chromosomal defect, three out of four mongol babies are bom to women under the age of 35 — simply because the majority of babies are bom to younger women. There is also a range of other defects involving missing, extra or rearranged chromosomes.

At present older women and those whose babies are at high risk of birth defects may be offered a more

complicated test involving the insertion of a needle into the mother’s abdomen and the withdrawal of a sample containing cells cast off from the baby. If, after further tests, these cells are found to be abnormal, many women choose an abortion. The potential risks of such a test do not justify its use in younger women, quite apart from its cost on a mass scale. The Stanford team’s external test uses an instrument called the fluorescence - activated cell sorter. Professor Howard Cann, a member of the team, explains that between two and 20 million foetal cells may cross the placenta and enter the mother’s bloodstream.

Babies’ cells carry material derived from the father, thus marking them out as different from the mother’s cells. This difference has been utilised to develop a harness method of coating the babies’ cells with fluorescent material. The cell sorter has a laser beam which is used to separate the “glowing” foetal cells from the mother’s.

The next step is to persuade the foetal cells to reproduce themselves under laboratory conditions so that the chromosomes may be examined for abnormalities at an early stage in pregnancy. Only when cells divide do the chromosomes “condense” enough to become visible. Dr Cann stresses that he does not want to minimise

the hurdles. He thinks that perhaps within two years “we will know whether or not the cells will divide.” All pregnant women in the study had foetal cells in their blood between 15 and 27 weeks of pregnancy. Dr Cann is optimistic that “many pregnant women will have the babies’ cells in their blood.” Once the cell culture techniques have been perfected, Dr Cann sees the test being used to screen younger women, with internal needle analysis as a back-up initially to confirm results indicating abnormality. Eventually it might be that the external test could take over prenatal diagnosis of birth defects in both older and younger women. The Stanford work raises further questions about a number of birth mysteries. For instance, how is it that the mother does not reject the baby if there are millions of foetal cells milling through the blood? Professor Cann speculates that perhaps there is a “blunted” immune response by the mother’s system to these particular cells.

What might be the function of these cells? Do they trigger off hormone responses in the mother? Professor Cann says: "We hope our work may help to provide an anwser. But for the moment we must be honest and say we haven’t the foggiest idea why these cells cross into the mother.”

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