for Down syndrome

First Trimester Screen | Fß

PerkinElmer Labs/NTD's First Trimester Screen | Fß test reliably assesses a mother's risk for having a baby with Down syndrome, trisomy 18 and 13 in the first trimester of pregnancy. Performed between 11 weeks, 1 day and 13 weeks, 6 days gestation, the First Trimester Screen | Fß uses data from a blood test (biochemistry) and an ultrasound examination (biophysical) which yields a risk assessment that physicians may present to their patients during the first trimester.

A maternal dried blood spot sample is analyzed for two biochemical markers: free beta human chorionic gonadotropin (free beta hCG) and pregnancy associated plasma protein-A (PAPP-A). Blood specimens are collected one of two ways, through a simple finger stick method, or with venipuncture. The venous blood is immediately spotted onto a dried blood spot card provided by PerkinElmer Labs/NTD using a Diff-Safe device or the blood is spotted directly from the finger.

The ultrasound examination confirms the fetus' gestational age and measures the nuchal translucency (NT), or the fluid accumulation behind the fetus' neck. These combined biochemical and biophysical markers yield the most sensitive screening results possible at the earliest point during the pregnancy, achieving a 91% detection rate at a 5% false positive rate for Down syndrome (and a 95% detection rate at a 0.3% false positive for trisomy 18 and 13). When a Fetal Nasal Bone Assessment is added to the protocol, the detection rate for Down syndrome increases to 95% at a false positive rate of just 2%.

(References 13,25,26)

Primary benefits of First Trimester Screen | Fß

• 91% detection rate, 5% false positive rate for Down syndrome (95% detection rate, 0.3% false positive rate for trisomy 18 and 13)
• Safe, simple, non-invasive test
• 95% of all patients are shown to be at low risk for Down syndrome which means early reassurance for the vast majority of your patients
• Those shown to be at higher risk can receive immediate counseling regarding possible follow up options such as CVS (chorionic villus sampling) and amniocentesis
• High detection rates reduce the number of missed cases
• Separate twin reports provided
• Separate interpretations for Down syndrome and trisomy 18 and 13 provided
• Reduces the potential for iatrogenic losses of unaffected fetuses

(References 13,26)

The advantages of free Beta hCG:

The use of free beta hCG in screening for Down syndrome and other chromosomal abnormalities during the first trimester has been demonstrated to be more effective than other markers, including intact or total hCG. Intact/total hCG, while an effective second trimester marker, is not considered effective during the first trimester. Laboratories that lack the technology to measure free beta hCG have attempted to use total hCG as part of their first trimester screening. This practice results in significantly higher false positive rates for Down syndrome as compared to protocols that measure free beta hCG.

(References 28)

The ACMG (American College of Medical Genetics) published technical guidelines on prenatal screening in September 2009. These guidelienes state:

"Before 11 weeks, free beta hCG is discriminatory but hCG is not. Between 11 and 13 gestational weeks, free beta hCG is univariately a more discriminatory Down syndrome screening marker than hCG."

(References 27)

Dried Blood Spot Advantages:

Logistical:

• No centrifugation or refrigeration necessary
• Eliminates possibility of broken sample tubes during transport
• Reduces biohazard risk
• Raises reporting reliability - blood sample, NT measurement and patient information are provided all on one card

Analytical:

• Stabilization of serum proteins
• Reduced analyte standard deviation