First trimester ultrasound screening is far from perfect.
For a 30-year old woman, the T21 detection rate is only 84%[1] - and the false positive rate is high at 4%. As age increases, so does the false positive rate - up to a whopping 67% at 49.
So even if you were told the test detected T13/18/21, a decision to terminate the pergancy could mean terminating a healthy fetus. A terrible decision to make.
But there is some better news - there is a relatively new screening test, the so called "Harmony Test", which is a type of non-invasive prenatal test (NIPT) that involves drawing blood from the mother and looking at the fetal DNA that is present[2]. For the most common genetic disorder, T21, the false positive rate is less than 0.1%[3], or 0.3% for all 3 disorders combined[4].
However, at least in the UK, the test is only available privately for around £400.
I didn't make clear in the first paragraph, but ultrasounds are screening tests, not diagnostic tests. The expensive blood tests are diagnostic.
Screening tests are inexpensive, low risk, high recall (i.e. high true positive) tests meant to indicate if high precision (i.e. low false positive, low false negative) test is warranted. Often the diagnostic tests are more invasive, potentially riskier, and more expensive.
For a 30-year old woman, the T21 detection rate is only 84%[1] - and the false positive rate is high at 4%. As age increases, so does the false positive rate - up to a whopping 67% at 49.
So even if you were told the test detected T13/18/21, a decision to terminate the pergancy could mean terminating a healthy fetus. A terrible decision to make.
But there is some better news - there is a relatively new screening test, the so called "Harmony Test", which is a type of non-invasive prenatal test (NIPT) that involves drawing blood from the mother and looking at the fetal DNA that is present[2]. For the most common genetic disorder, T21, the false positive rate is less than 0.1%[3], or 0.3% for all 3 disorders combined[4].
However, at least in the UK, the test is only available privately for around £400.
[1] https://www.ncbi.nlm.nih.gov/pubmed/11702835
[2] https://fetalmedicine.com/harmony-test
[3] https://sequencing.roche.com/en/healthcare-providers/nipt/fa...
[4] http://www.rapid.nhs.uk/guides-to-nipd-nipt/nipt-for-down-sy...