TEALE FENNING

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

Sonographic scoring for Down syndrome

Marker

Likelihood ratio

Ref:- Nicolaides et al

Normal examination

0.4

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

Point system for sonographic markers of Down syndrome
Marker

Points

EMAK · Century Club Joined: 26 Nov 2006 Posts: 572

what about serum markers or tests? we can start to justify each one saparatelly ?Cpeed. Cool

Nick Raine-Fenning · Posted: Sat Sep 08, 2007 10:25 am Post subject:

Asha - can you clarify the difference between the 'marker points' and 'marker - likihood ratio' systems for everyone (including me Wink

)

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

Large number of markers for Down syndrome and controversy regarding how to best implement them led to the development of the "genetic sonogram"

tool for sonographic risk assessment of Down syndrome.

One type of genetic sonogram calculates likelihood of Down syndrome based upon presence of markers and maternal age. As an example, a case-control study compared 142 fetuses with Down syndrome to 930 control fetuses with normal karyotype. Fetal risk of Down syndrome was derived from multiplying the a priori risk, based upon maternal age, with likelihood ratios determined from the presence or absence of specific sonographic findings for each patient.

Among women under 35 years of age, 62 % Down syndrome were identified.

Among women 35 to 39 and 40 years of age, the sensitivity was 67 % 100 %, respectively.

Among fetuses with a normal karyotype, the screen positive rate in these three age groups was 4, 13, and 100 %, respectively.

A completely normal sonogram (containing no markers for Down syndrome) reduced the maternal-age related risk of Down syndrome by 60 %.

Ultrasound examination can be useful for detecting Down syndrome in young women and avoiding invasive procedures in women between 35 and 39 years of age whose sonogram puts them at low risk of having an affected baby.

However, all women 40 years of age require invasive testing to determine fetal karyotype, regardless of the ultrasound findings, because of the high incidence of Down syndrome at very advanced maternal ages.

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

Integrative testing, which combines nuchal translucency measurements with serum markers drawn in the first and second trimester,

most efficient means of detecting Down syndrome.

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

Summary —

Initially, detection of Down syndrome - primarily based upon screening by maternal age: amniocentesis offered primarily to women 35y and more. This protocol detected 20% of affected pregnancies.

The addition of the triple maternal analyte screen increased the detection rate to 60 to 65%.

Adding a genetic sonogram alone or incorporating results of triple test + genetic sonogram

detection rates of 75 to 90 %;highest sensitivity in women 35 years old. This multimodal approach improved the detection rate of Down syndrome in younger women's pregnancies and provided women aged 35 years with better information upon which to compare the risk of amniocentesis versus the risk of an affected pregnancy.

Integrative testing, which combines nuchal translucency measurements with serum markers drawn in the first and second trimester,

most efficient means of detecting Down syndrome.

Women with abnormal integrative testing should undergo fetal karyotype testing even if their genetic sonogram is normal.

There is insufficient evidence to recommend fetal karyotype testing if the genetic sonogram is abnormal but integrative testing is normal.

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

A good article

Nuchal translucency and other first-trimester sonographic markers of chromosomal abnormalities
American Journal of Obstetrics and Gynecology, Volume 191, Issue 1, July 2004, Pages 45-67
Kypros H. Nicolaides

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

To clarify marker -likelihood ratos-- I guess we will have to discuss the term likelihood ratio, positive likelihood artio, negative likelihood ratio etc in detail. Not sure we can do this on this thread -- but shall do it later .

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

In each case, the likelihood ratio is derived by dividing the incidence of a given marker in trisomy 21 pregnancies by its incidence in chromosomally normal pregnancies.

Eg- Intracardiac echogenic focus found in 28.2% of trisomy 21 fetuses and in 4.4% chromosomally normal fetuses,

positive likelihood ratio of 6.41 (28.2/4.4) and a negative likelihood ratio of 0.75 (71.8/95.6).

Consequently, the finding of an echogenic focus increases the background risk by a factor of 6.41, but at the same time an absence of this marker should reduce the risk by 25%.

cpeedahsa · Century Club Joined: 21 Apr 2007 Posts: 921

For example, in a 32-year-old woman at 20 weeks of gestation (background risk, 1 in 507) who had an NT screening that resulted in a 7-fold reduction in risk (to 1 in 3549), after the diagnosis of isolated echogenic bowel at the 20-week scan, the estimated risk would increase by a factor of 3 to 1 in 1183.

However, for the same ultrasound finding in the absence of previous NT screening, the risk would increase from 1 in 507 to 1 in 169.