Limits...
Evaluation of a proposed mixture model to specify the distributions of nuchal translucency measurements in antenatal screening for Down's syndrome.

Bestwick JP, Huttly WJ, Wald NJ - J Med Screen (2010)

Bottom Line: A mixture model of crown-rump length (CRL)-dependent and CRL-independent nuchal translucency (NT) measurements has been proposed for antenatal screening for Down's syndrome.Settings A routine antenatal screening programme for Down's syndrome comprising 104 affected and 22,284 unaffected pregnancies.Risk estimation was marginally (but not statistically significantly) more accurate using the standard MoM method.

View Article: PubMed Central - PubMed

Affiliation: Wolfson Institute of Preventive Medicine, Barts and the London Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, UK. j.p.bestwick@qmul.ac.uk

ABSTRACT

Objectives: A mixture model of crown-rump length (CRL)-dependent and CRL-independent nuchal translucency (NT) measurements has been proposed for antenatal screening for Down's syndrome. We here compare the efficacy of the mixture model method with the standard method, which uses NT multiple of the median (MoM) values in a single distribution. Settings A routine antenatal screening programme for Down's syndrome comprising 104 affected and 22,284 unaffected pregnancies.

Methods: The ability of NT to distinguish between affected and unaffected pregnancies was compared using the mixture model method and the standard MoM method by using published distribution parameters for the mixture model of NT and parameters derived from these for the standard MoM method. The accuracy of the two methods was compared for NT and maternal age by comparing the median estimated risk with the prevalence of Down's syndrome in different categories of estimated risk.

Results: Using NT alone observed estimates of discrimination using the two methods are similar; at a 70% detection rate the false-positive rates were 12% using the mixture model method and 10% using the MoM method. Risk estimation was marginally (but not statistically significantly) more accurate using the standard MoM method.

Conclusions: The mixture model method offers no advantage over the standard MoM method in antenatal screening for Down's syndrome, is more complicated and less generalizable to other data-sets. The standard MoM method remains the method of choice.

Show MeSH

Related in: MedlinePlus

Mixture model distributions of nuchal translucency (NT) in mm and distributions of NT multiple of the median (MoM) values in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation. Truncation limits shown (vertical lines) are those specified by Wright et al.1
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3104819&req=5

JMS-09108F1: Mixture model distributions of nuchal translucency (NT) in mm and distributions of NT multiple of the median (MoM) values in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation. Truncation limits shown (vertical lines) are those specified by Wright et al.1

Mentions: Figure 1 shows the relative frequency distributions of NT in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation together with truncation limits using the mixture model method and the standard MoM method (the parameters [means and standard deviations] of the mixture model method distributions and standard MoM method distributions are given in Appendix B, Table B1). With the mixture model method the distribution in affected pregnancies remains approximately stationary from week to week while the distribution in unaffected pregnancies moves to the right as gestation increases. With the standard MoM method the distribution in affected pregnancies moves to the left with increasing gestation while the distribution in unaffected pregnancies remains stationary. Figure 1 shows that the mixture distributions are similar to the MoM distributions, i.e. since the proportion of unaffected pregnancies that have CRL-independent NT and the proportion of affected pregnancies that have CRL-dependent NT are low the mixture distributions closely resemble the Gaussian distributions of NT MoM values.


Evaluation of a proposed mixture model to specify the distributions of nuchal translucency measurements in antenatal screening for Down's syndrome.

Bestwick JP, Huttly WJ, Wald NJ - J Med Screen (2010)

Mixture model distributions of nuchal translucency (NT) in mm and distributions of NT multiple of the median (MoM) values in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation. Truncation limits shown (vertical lines) are those specified by Wright et al.1
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104819&req=5

JMS-09108F1: Mixture model distributions of nuchal translucency (NT) in mm and distributions of NT multiple of the median (MoM) values in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation. Truncation limits shown (vertical lines) are those specified by Wright et al.1
Mentions: Figure 1 shows the relative frequency distributions of NT in Down's syndrome and unaffected pregnancies at 11, 12 and 13 completed weeks' gestation together with truncation limits using the mixture model method and the standard MoM method (the parameters [means and standard deviations] of the mixture model method distributions and standard MoM method distributions are given in Appendix B, Table B1). With the mixture model method the distribution in affected pregnancies remains approximately stationary from week to week while the distribution in unaffected pregnancies moves to the right as gestation increases. With the standard MoM method the distribution in affected pregnancies moves to the left with increasing gestation while the distribution in unaffected pregnancies remains stationary. Figure 1 shows that the mixture distributions are similar to the MoM distributions, i.e. since the proportion of unaffected pregnancies that have CRL-independent NT and the proportion of affected pregnancies that have CRL-dependent NT are low the mixture distributions closely resemble the Gaussian distributions of NT MoM values.

Bottom Line: A mixture model of crown-rump length (CRL)-dependent and CRL-independent nuchal translucency (NT) measurements has been proposed for antenatal screening for Down's syndrome.Settings A routine antenatal screening programme for Down's syndrome comprising 104 affected and 22,284 unaffected pregnancies.Risk estimation was marginally (but not statistically significantly) more accurate using the standard MoM method.

View Article: PubMed Central - PubMed

Affiliation: Wolfson Institute of Preventive Medicine, Barts and the London Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, UK. j.p.bestwick@qmul.ac.uk

ABSTRACT

Objectives: A mixture model of crown-rump length (CRL)-dependent and CRL-independent nuchal translucency (NT) measurements has been proposed for antenatal screening for Down's syndrome. We here compare the efficacy of the mixture model method with the standard method, which uses NT multiple of the median (MoM) values in a single distribution. Settings A routine antenatal screening programme for Down's syndrome comprising 104 affected and 22,284 unaffected pregnancies.

Methods: The ability of NT to distinguish between affected and unaffected pregnancies was compared using the mixture model method and the standard MoM method by using published distribution parameters for the mixture model of NT and parameters derived from these for the standard MoM method. The accuracy of the two methods was compared for NT and maternal age by comparing the median estimated risk with the prevalence of Down's syndrome in different categories of estimated risk.

Results: Using NT alone observed estimates of discrimination using the two methods are similar; at a 70% detection rate the false-positive rates were 12% using the mixture model method and 10% using the MoM method. Risk estimation was marginally (but not statistically significantly) more accurate using the standard MoM method.

Conclusions: The mixture model method offers no advantage over the standard MoM method in antenatal screening for Down's syndrome, is more complicated and less generalizable to other data-sets. The standard MoM method remains the method of choice.

Show MeSH
Related in: MedlinePlus