Scientific Evidence

What data is available to support first trimester screening?

The effectiveness of first trimester screening utilizing NT measurement and 2 biochemical markers, free Beta-hCG and PAPP-A, has been proven in over 20 worldwide studies totaling over 200,000 patients. The detection rate is about 90% at a 5% false positive rate.1 When the nasal bone measurement is included, the detection rate is 95% at a 2% false positive rate.2

Click here for published studies.

What are the most effective biochemical markers for first trimester screening?

The most effective biochemical markers for first trimester screening are free Beta-hCG and pregnancy associated plasma protein A. Together these 2 markers can detect about 63% of Down syndrome cases.3 With the inclusion of nuchal translucency about 90% of Down syndrome cases can be detected with the screening procedure1, and with the addition of the nasal bone measurement, about 95% of cases are detected.2

Is total hCG an effective marker in first trimester screening?

Total hCG is not effective in first trimester screening. To maximize the benefits of first trimester screening, free Beta-hCG must be used instead of total hCG.

Some laboratories which lack the technology to measure free Beta-hCG are attempting to use total hCG in first trimester screening. These laboratories will detect significantly fewer cases of Down syndrome than those laboratories using free Beta-hCG. Free Beta-hCG and total hCG are not the same.


1 Avgidou, K.,et al. (2005) American Journal of Obstetrics and Gynecology 192: 1761-7.
2 Cicero, S., et al. (2003) Ultrasound in Obstetrics and Gynecology 22(1): 31-5.
3 Krantz, D.A., et al. (1996) American Journal of Obstetrics and Gynecology 174(2): 612-616.