Mr. Peter Thompson:

In the UK, women have scans at 12 weeks, which is predominantly for dating. In addition, women are offered that test as part of a combined screening test that measures age, the thickness at the back of the foetus's neck - the so-called nuchal translucency - and markers of hormones in the woman's bloodstream. That will give the likelihood of the risk of the baby having Down syndrome, Edwards syndrome or Patau syndrome. One does not have to have that test. In our unit, only about 60% to 70% of women take up that test but they still have the scan for viability. In addition to that, women get a detailed anomaly scan between 18 and 22 weeks, which most units try to perform at about 20 weeks.