First Trimester Screening
First trimester screening is a screening test for Trisomy 21 (Down’s syndrome), Trisomy 18 (Edward’s Syndrome) and Trisomy 13 (Patau’s syndrome). A combination of age, ultrasound and blood test results are used to give women a risk for the above mentioned syndromes. If blood test results are available the risk is calculated and the patient counselled with the results.
The high risk cut off is 1:300 for Trisomy 21 and 1:150 for Trisomy 13 and 18. A “high risk” result does not mean your fetus has a chromosome abnormality but you are in the group of women to whom further testing is recommended. It is a screening not a diagnostic test.
The ultrasound software license is provided by the Fetal Medicine Foundation. All our sonographers are accredited and required to perform an annual audit (RANZCOG), to ensure high standards are maintained.
The ultrasound component of the test involves measuring the nuchal translucency (or fluid filled area at the back of the fetuses neck), assessing growth and other structures. The nuchal translucency should be thin at this stage.
This test can be performed between 11 ½ weeks and 13 weeks and 6 days gestation – the fetal crown rump length being between 45 and 84 mm.