The chance of a child with Down’s Syndrome is higher when the pregnancy occurs at a later age. Every pregnant woman has such a chance however, regardless of age. The table below is shows an indication of the chances at each age.
Age of the mother with chance of a child with Down’s Syndrome:
20 – 25 years old: 11 to 13 of 10.000
26 – 30 years old: 14 to 19 of 10.000
31 – 35 years old: 20 to 45 of 10.000
36 – 40 years old: 60 to 155 of 10.000
41 – 45 years old: 200 to 615 of 10.000
This is a general chance and thus not specific, so a pregnant woman can choose to calculate the chance for her child specifically. This is done through the combination test.
The combination test examines the chance of whether the unborn child has a risk of Down’s, Edward’s or Pataus Syndrome during the early pregnancy (first trimester). The test does not carry additional risks.
The combination test is consists of two tests:
• A blood test of the pregnant woman during the period of 9 to 14 weeks (specifically 13 weeks and 6 days into the pregnancy);
• The nuchal translucency of the unborn child. This is done via an echo which is made in the period of 11 to 14 weeks into the pregnancy.
The blood test examines the values of the (blood) serum of the PAPP-A (pregnancy associated plasma protein A) and f ß-hCG (free ß subunit of choriongonadotrophin).
Subsequently, a biochemical value is determined based on the following characteristics of the woman: the age of the one pregnant, their weight, whether they are a smoker and the period of pregnancy at the moment the blood test is done.
The nuchal translucency is tested through an echo which done at our practice. The nuchal translucency is a thin moisture layer in the neck and underneath the skin. This layer is present in each child, including healthy ones. The thicker the nuchal translucency the larger the chance of a child with Down’s Syndrome.
By combining the serum values with the nuchal translucency tests, the specific chances of the child having Down’s, Edward’s and/or Pataus Syndrome is calculated.
If the chances are higher than 1:200 (so for example, 1:150), then there is a higher risk. In this case you can opt for a follow-up examination. If the chances are lower than 1:200, then a low chance of the syndromes is expected.
The combination test gives, aside from the chance of a child with Down’s Syndrome, additional information about the chances of Pataus Syndrome (trisomy 13) and Edward’s Syndrome (trisomy 18). These are congenital disorders, like Down’s Syndrome. These disorders are also caused by an additional chromosome. A child with Pataus Syndrome doesn’t have two but three chromosome 13 in each cell, and a child with Edward’s Syndrome has three copies of chromosome 18. Both Pataus and Edward’s Syndrome are much less common than Down’s.
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The follow-up examination may comprise of a NIPT (Non-Invasive Prenatal Test) as of 10 weeks into the pregnancy, a CVS (between 11 and 14 weeks pregnant) or an amniocentesis (after 16 weeks pregnancy).
Both the CVS and the amniocentesis carry a small risk of miscarriage as a result of the examination. This happens in 3-5 out of 1000 tests. The NIPT is a blood test whereby the DNA of the fetus is examined for trisomy 13, 18 and 21 and carries no risk of a miscarriage. In the Netherlands the NIPT is only done if the results of the combination test indicate an increased risk. Should you wish to do a NIPT before having done a combination test, then please inform about the possibilities during your first interview.