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The 11-13 weeks scan

Welcome to this educational course of the Fetal Medicine Foundation on the 11-13 weeks scan

The Fetal Medicine Foundation, which is a charitable organization, will continue to work for the benefit of pregnant women and their families. We:

  • Support research into better methods of prenatal diagnosis
  • Provide training of doctors on an international basis
  • Give up-to-date information for pregnant women and health care professionals

The traditional method of screening for Down’s syndrome has been maternal age where amniocentesis or chorionic villous sampling is offered to women aged 35 years or more. This results in the need for an invasive test in 15-20% of pregnant women with a detection of less than half of the fetuses with Down’s syndrome, because the majority of affected fetuses come from the younger age group

A more effective method of screening is based in the combination of:

  • Maternal age
  • A maternal blood sample for the measurement of the placental products of free ß-hCG and PAPP-A
  • An ultrasound scan at 11-13 weeks:
    • to measure the collection of fluid behind the fetal neck (nuchal translucency)
    • to examine the fetal nose and palate
    • to measure the fetal heart rate
    • to assess the flow of blood across the tricuspid valve of the fetal heart and the ductus venosus

This new method of screening reduces dramatically the number of women requiring an invasive test from about 20% to less than 3% and at the same time increases the detection rate of Down’s syndrome and other major chromosomal abnormalities from less than 50% to more than 95%

Other benefits of the 11–13 weeks scan include:

  • Accurate dating of the pregnancy
  • Early diagnosis of many major fetal abnormalities
  • The detection of multiple pregnancies with reliable diagnosis of chorionicity, which is the main determinant of the outcome in multiple pregnancies
  • Another recent development is that the 11-13 weeks scan can be used to identify women at increased risk for the development of preeclampsia in pregnancy

Although there are many benefits from the 11-13 weeks scan it is essential that those undertaking this examination have a good knowledge of the diagnostic features and management of the conditions identified by this scan are adequately trained to perform the scan to a high standard, and their results are subjected to ongoing quality assurance based on the distribution of their measurements and examination of a sample of their images

I hope that you find the information provided useful and I would welcome any suggestions that would help improve the course