When can this scan be done:
20 – 22 Weeks:
The aims of the scan:
- To assess the growth of the baby;
- To determine the amniotic fluid volume;
- To check if the placenta/afterbirth is in the correct position for vaginal delivery;
- To assess for structural/physical abnormalities like for instance cleft lip and palate, heart defects, club feet etc. Approximately 1% of babies are born with a physical abnormality. If a physical abnormality is detected, referral may be made to a specialist for a second opinion and further evaluation;
- To assess the blood flow from the mother to the baby;
- If opted for, to assess the risk for Downs syndrome.
If the earlier 12 – 13 week Nuchal translucency scan was done, 9 markers for Downs syndrome will be checked and the risk for Downs syndrome will be adjusted only if markers are found.
If a second trimester blood test (Triple test) was done for Downs syndrome, the blood results combined with the absence or presence of markers will then determine the adjusted risk for Downs syndrome. The detection rate for Downs syndrome with a Triple test and Detail scan combined is approximately 65 – 70%.
If only markers are checked without previous scan or blood tests, the detection rate for Downs syndrome is only 60 %.
The risk categories remain the same as in the first trimester. 1:2 to 1:300 is high risk; 1:300 – 1:1 000 is intermediate risk and a number above 1:1 000 is low risk for Downs syndrome. If we are worried at this point about Downs syndrome there are other tests available with better detection rates than any scan at any time can provide. These tests are as always optional:
- Non-invasive prenatal testing (NIPT) is a blood test on the mother and therefore carries no risk of miscarriage. The detection rate for Downs syndrome is 99.8%. Unfortunately, this test is still expensive in South Africa, approximately R2 500 – R6 500.
- Invasive testing carries a small risk for miscarriage, approximately 1:300. An amniocentesis can be done from 16 weeks onwards and the detection rate for Downs syndrome is 99.99% and we therefore call it a diagnostic test.
Fetal View does not offer invasive testing. We can refer you for this test if you would like.