13 Weeks with Down Syndrome Screening/ Post NIPT
Why have a scan at 12-13 weeks?
It has been shown that a high proportion of fetuses with a chromosomal abnormality such as Down syndrome can be suspected at an ultrasound examination at 13 weeks. All fetuses at 13 weeks retain small amounts of fluid under the skin around the head and neck, but this is usually slightly increased when Down syndrome is present. This is not an “abnormality” because the fluid is absorbed during the pregnancy. Additional fluid therefore does no harm but can be used as a marker for Down syndrome. Fluid under the skin looks black on ultrasound, and we measure the “nuchal translucency” or black area, when this area is thickened it is called “nuchal oedema” (or swelling behind the neck).
This scan is also performed after the percept™ NIPT test to detect any physical abnormalities possible with ultrasound at this stage.
Click below to find out more about the percept™/NIPT test offered by VCGS.
Who will carry out the scan?
The operation is performed by a sonographer (an ultrasound technologist). The results are assessed using soft-ware developed in London by Professor Nicolaides of the Fetal Medicine Foundation. Melbourne Ultrasound for Women are the Victorian Training Centre for the Foundation. We have continuous ongoing audit to ensure that all operators at Melbourne Ultrasound for Women continue to obtain reproducible measurements. At the end of the examination you will be told whether we consider the result
to be high or low risk and these results will be sent to your doctor.
Can I discuss the results in detail with a staff member?
If your doctor has referred you to this practice for counselling as well as an ultrasound examination, you may see one of our Doctors to discuss not only the results but also options for further testing.
Pregnant women who wish to exclude chromosome abnormality can choose to have amniocentesis or CVS. What we can do however, using software developed by the Fetal Medicine Foundation in London, is tell pregnant women the risk that their fetus has a chromosome abnormality. This is calculated from their age, the thickness of the “nuchal translucency”, and the number of weeks pregnant they are (because the thickness varies with the number of weeks).
The benefits of a scan at this stage include:
• Highest detection rate of any “no risk” or screening test for chromosome
abnormality (including Down syndrome)
• Accurate dating of the pregnancy
• Diagnosis of multiple pregnancy
• Diagnosis of early pregnancy failure (at 12 weeks approximately 1 in 50
women are found on ultrasound to have a failed pregnancy)
• Detection of many physical abnormalities is possible with ultrasound at
When should the scan be carried out?
The scan is best performed at 13 weeks. If the pregnancy is found to be less advanced that expected then rescheduling may be required. This scan is also performed after the percept™ NIPT test.
Will the scan be carried out through the abdomen or
through the vagina?
For 9 out of 10 patients the measurements of the nuchal translucency can be carried out with a scan through the abdomen, so this will be the first part of the examination. If the measurement could be carried out better through the vagina then you would be offered this method (of course you are always free to refuse any examination you do not wish to have). Having finished the scan through the abdomen most women will be offered an additional scan through the vagina since this usually gives better images of
the fetus, and therefore offers a better chance of detecting any physical abnormality. Physical abnormalities are usually best detected at 18-20 weeks, however many abnormalities can be detected at this early stage, particularly with a vaginal scan.