• Question: How does a doctor know when a foetus has a symptom (e.g. Down Syndrome) before birth?

    Asked by doubleu to Damien, Rachael, Simon, Suzi, Tim on 21 Jun 2011.
    • Photo: Suzi Gage

      Suzi Gage answered on 21 Jun 2011:

      Hi @doubleu
      Thanks for this question. When a foetus is still in the womb, a sample can be taken from it using a long needle which goes through the Mum to get to the foetus, and this can be analysed for any genetic illnesses, like Downs Syndrome.
      These tests cannot be done before a foetus is 9.5 weeks. It is a risky thing to do as it can increase the chance of a miscarriage, but if the family believe there is a chance the baby will be born with genetic problems, it can be a worthwhile thing to do because then the family can decide whether to have the baby, and if they do decide to have it, they are prepared for it’s illness when it is born.

      What do you think about this?

    • Photo: Tim Fosker

      Tim Fosker answered on 21 Jun 2011:

      Hi @doubleu

      My wife and I have a baby due in October, so we have been to the hospital several times for her to have tests. The amniocentesis test that Suzi describes (where a needle is used to take fluid from the amniotic sack where the baby is) is a diagnostic test, meaning it is quite accurate. However there are screening tests for things like Down’s syndrome. Screening tests are not as accurate as diagnostic tests as they measure ‘markers’ of a syndrome. By markers I mean some kind of measurement that is related to a disorder and predicts its occurrence. One marker for Down’s syndrome is fluid build-up at the back of the baby’s neck that can sometimes be seen on an ultrasound scan. There are also specific proteins that if higher than normal in the blood suggest that a baby may have Down’s syndrome. There are groups of scientists that work very hard to find markers for different syndromes that babies can be born with, it is a very important area of research.

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