Scientific evidence demonstrates that free beta human Chorionic Gonadotropin (hCG) is consistently significantly elevated in Down syndrome cases. A review of 21 retrospective studies involving 772 reported Down syndrome cases shows that free beta hCG was on average 2.0 Multiples of the Median (MoM), or significantly deviated from normal levels in Down syndrome cases, and thus an excellent Down syndrome marker. An alternative protocol replaces free Beta hCG with total, or intact, hCG. However, the data on total hCG does not support its use as a first trimester marker for Down syndrome. A review of 15 retrospective studies showed that total hCG was, on average, only 1.29 MoM, or slightly elevated in Down syndrome cases, and therefore, not a reliable Down syndrome marker in the first trimester. Substituting total hCG for free beta hCG may lead to potential Down syndrome cases going undetected and/or result in higher false positive rates. (References 28) This, in turn, may increase the performance of unnecessary diagnostic procedures and therefore may also increase the iatrogenic losses of unaffected fetuses.
The ACMG (American College of Medical Genetics) published technical guidelines on prenatal screening in September 2009. These guidelines 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)
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