Baby's sex test offers new hope
- By Julie Robotham Medical
Editor
December 7, 2005
AUSTRALIAN doctors have identified the sex of 22 foetuses as early as five
weeks into pregnancy from cells taken from their mother's cervix, in a "proof of
concept" experiment they say could lead to improved tests for conditions such as
Down syndrome and cystic fibrosis.
Gab Kovacs, professor of obstetrics and gynaecology at Melbourne's Box Hill
Hospital, said women would welcome the opportunity to know their foetus was
healthy as early as possible during pregnancy.
Where an abnormality was detected and the woman chose termination, this would
involve fewer risks and medical complications if it could be done earlier. At
present, the earliest test that can determine definitively if a foetus is
affected by Down syndrome is chorionic villus sampling, in which placental cells
are cultured around 11 weeks of pregnancy. But the test is invasive, and
occasionally triggers miscarriage of healthy foetuses. Amniocentesis, conducted
later in pregnancy, has similar drawbacks.
Professor Kovacs's initial study, reported this week in the Australian and
New Zealand Journal of Obstetrics and Gynaecology, was carried out in women
who were having abortions. The scientists compared the sex of the foetus
identified from foetal cells in the women's cervical mucus with the sex
chromosomes they found in the placenta after the termination. The results
matched in all cases.
The next phase would be to conduct a larger study in women who were
continuing their pregnancies, Professor Kovacs said. This would provide extra
information about the reliability of the method, which uses polymerase chain
reaction (CVS) technology to confirm the cells are not from the mother and the
sex of the foetus. "We have ethics committee approval to do that in an antenatal
population," Professor Kovacs said. Detecting abnormalities would be no more
difficult technically than determining sex, he said.
The trial would also confirm the technique - which Professor Kovacs described
as causing "less discomfort than a Pap smear" - was safe for the mothers and
babies. But it would be at least five years before it could go into widespread
use.
Andrew McLennan, a consultant in foetal medicine at Royal North Shore
Hospital, said previous attempts to isolate foetal cells had failed, and
Professor Kovacs's technology was still at a very early stage.
If the new technique proved effective, Dr McLennan predicted it would
initially be used with more traditional tests.
A woman whose cervical mucus test showed she was at increased likelihood of
having a baby with an abnormality could be referred for amniocentesis or CVS, he
said, while women with more reassuring early results might opt not to have
further testing.
Australian statistics show that more than 90 per cent of women whose foetus
is diagnosed with Down syndrome choose to terminate the
pregnancy.