First Trimester Screening is a test for Trisomy 21 (Down Syndrome), Trisomy 18 (Edwards Syndrome) and Trisomy 13 (Patau Syndrome). The test uses software by license from the Fetal Medicine Foundation. It uses a combination of background factors (predominantly age), ultrasound and biochemistry to give the pregnant woman a risk for the conditions listed above. If biochemistry is available, the results are given immediately after the ultrasound, and appropriate counselling will be undertaken. Each sonographer is subject to regular audit of their performance in order to maintain standards. The audit is operated by RANZCOG.
For Trisomy 21, a risk of 1:300 or more is considered “high risk”. For Trisomy 13 and 18, a risk of 1:150 is considered “high risk”.
It is important to remember that First Trimester Screening is a test, not a diagnostic test. This is merely a guide as to whether further testing is warranted. This will be dependent on many factors, including the actual risk (eg 1:2 vs 1:299) and patient factors. Our doctors and trained sonographers will provide individualised counselling to help with the decision making process once a risk has been given, as every woman has different circumstances.
