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TESTS on fetal cells isolated from the mother’s blood in the first eight
weeks of pregnancy have revealed the sex of the fetus. The techniques, described
in The Lancet (28 July p 197), may also provide a way of identifying fetuses
suffering from serious genetic diseases without risking the mother or a
healthy fetus.

Other, ‘invasive’ techniques, such as amniocentesis and chorionic villus
sampling (CVS), carry a small (between 1 and 2 per cent) risk that the fetus
will abort spontaneously after the diagnostic procedure.

‘We now have the basis for routine prenatal screening programmes to
spot a range of genetic disorders such as Down’s syndrome and cystic fibrosis
as early as six weeks after conception,’ says Warren Jones, professor of
obstetrics and gynaecology at Flinders University in Adelaide and one of
the authors of the study.

The fetal cells in question are from the trophoblast, which forms the
wall of the blastocyst, the hollow ball of cells which is the early embryo.
Using monoclonal antibodies (MCAbs), Utz Mueller and his colleagues in Adelaide
isolated the fetal cells from blood samples by getting the cells to stick
to tiny magnetic beads coated with MCAbs derived from mice. Five such antibodies,
out of 6800 tested, bound tightly to the human trophoblast cells.

The genetic material from the cells, which is present in maternal blood
in relatively small quantities, was then replicated using the polymerase
chain reaction (PCR), a method of amplifying DNA exponentially. This is
so effective that the researchers could detect the male-determining Y-chromosome
from as few as three fetal white blood cells.

Until now, trophoblast cells for genetic analysis have been extracted
via a flexible tube inserted into the pregnant woman’s uterus, a technique
called chorionic villus sampling (CVS). The technique, which is used to
detect genetic disorders such as Down’s syndrome, carries a small risk to
the mother and healthy fetus. Amniocentesis, an alternative test that extracts
fetal cells from the amniotic fluid at about 18 weeks of pregnancy, also
carries a small risk.

Mueller’s study involved 12 women who had agreed to undergo CVS in early
pregnancy. Blood samples were taken first to avoid the possible release
of trophoblast cells into the circulation by the CVS. They then compared
the results of the tests on cells obtained by the two techniques. ‘We were
able to isolate the fetal cells as distinct from showing they are present,’
said Mueller. ‘It’s one thing to show they are there, it’s entirely another
thing to get them out.’

Tests on 11 of the 12 women correctly predicted the sex of seven male
and four female babies. But in one case the results of the blood test were
at odds with the CVS test. The researchers suspect that this was due to
contamination of the PCR procedure in the laboratory.

So before the test becomes routine, scientists and doctors will have
to organise trials to compare the accuracy of the new technique with the
conventional methods of CVS and amniocentesis, says Mueller. But plans for
marketing the test are already well underway. John Turner, head of Flinders
Technologies, said that the new test was one of the ‘most exciting dev elopments,
both technically and commercially, that I have ever encountered’.

Turner estimates that the new test, which relies on the specificity
of the monoclonal antibodies, could be ready for commercial use in about
two years. It should be worth Dollars A250 million (about Pounds sterling
125 million) a year. His company has the rights to commercialise the technology,
but is looking for investors abroad who could tackle the international market.

‘Already we have received expressions of interest from major organisations,’
said Turner. Patent applications have been taken out in all the major countries
of the world, he added.