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Distribution of nuchal translucency in antenatal screening for Down's syndrome.

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

Bottom Line: The screening performance of the Combined and Integrated tests (that include NT measurement) were compared using previous and revised estimates of the standard deviation.The standard deviation of NT in unaffected pregnancies has reduced over time (from 1998 to 2008) (e.g. from 0.1329 to 0.1105 [log(10) MoM] at 12-13 completed weeks of pregnancy, reducing the variance by about 30%).Compared with results from the serum, urine and ultrasound screening study (SURUSS), use of the revised NT standard deviations in unaffected pregnancies resulted in an approximate 20% decrease in the false-positive rate for a given detection rate; for example, from 2.1% to 1.7% (a 19% reduction) at a 90% detection rate using the Integrated test with first trimester markers measured at 11 completed weeks' gestation and from 4.4% to 3.5% (a 20% reduction) at an 85% detection rate using the Combined test at 11 completed weeks.

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

Objective: To determine whether the standard deviation of nuchal translucency (NT) measurements has decreased over time and if so to revise the estimate and assess the effect of revising the estimate of the standard deviation on the performance of antenatal screening for Down's syndrome.

Setting: Data from a routine antenatal screening programme for Down's syndrome comprising 106 affected and 22,640 unaffected pregnancies.

Methods: NT measurements were converted into multiple of the median (MoM) values and standard deviations of log(10) MoM values were calculated in affected and unaffected pregnancies. The screening performance of the Combined and Integrated tests (that include NT measurement) were compared using previous and revised estimates of the standard deviation.

Results: The standard deviation of NT in unaffected pregnancies has reduced over time (from 1998 to 2008) (e.g. from 0.1329 to 0.1105 [log(10) MoM] at 12-13 completed weeks of pregnancy, reducing the variance by about 30%). This was not observed in affected pregnancies. Compared with results from the serum, urine and ultrasound screening study (SURUSS), use of the revised NT standard deviations in unaffected pregnancies resulted in an approximate 20% decrease in the false-positive rate for a given detection rate; for example, from 2.1% to 1.7% (a 19% reduction) at a 90% detection rate using the Integrated test with first trimester markers measured at 11 completed weeks' gestation and from 4.4% to 3.5% (a 20% reduction) at an 85% detection rate using the Combined test at 11 completed weeks.

Conclusions: The standard deviation of NT has declined over time and using the revised estimates improves the screening performance of tests that incorporate an NT measurement.

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Probability plots of nuchal translucency in unaffected pregnancies according to week of gestation
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JMS-09107F2: Probability plots of nuchal translucency in unaffected pregnancies according to week of gestation

Mentions: Figure 1 shows the relative frequency distributions of NT in Down's syndrome and unaffected pregnancies using previous estimates of the standard deviation in unaffected pregnancies and revised estimates at 11, 12 and 13 completed weeks' gestation. As a single screening test considered without maternal age, NT alone has revised detection rates of 71%, 68% and 61% for a 5% false-positive rate at 11, 12 and 13 completed weeks, respectively, compared with previous estimates of 67%, 63% and 55%, respectively.1 Truncation limits for NT (also given in Table 2) were revised based on probability plots of NT MoM values (see Figure 2) and to prevent the reversal of risk at lower NT MoM values4 (i.e. risk of Down's syndrome decreasing with smaller NT measurements and then increasing with further decreases in NT).


Distribution of nuchal translucency in antenatal screening for Down's syndrome.

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

Probability plots of nuchal translucency in unaffected pregnancies according to week of gestation
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104820&req=5

JMS-09107F2: Probability plots of nuchal translucency in unaffected pregnancies according to week of gestation
Mentions: Figure 1 shows the relative frequency distributions of NT in Down's syndrome and unaffected pregnancies using previous estimates of the standard deviation in unaffected pregnancies and revised estimates at 11, 12 and 13 completed weeks' gestation. As a single screening test considered without maternal age, NT alone has revised detection rates of 71%, 68% and 61% for a 5% false-positive rate at 11, 12 and 13 completed weeks, respectively, compared with previous estimates of 67%, 63% and 55%, respectively.1 Truncation limits for NT (also given in Table 2) were revised based on probability plots of NT MoM values (see Figure 2) and to prevent the reversal of risk at lower NT MoM values4 (i.e. risk of Down's syndrome decreasing with smaller NT measurements and then increasing with further decreases in NT).

Bottom Line: The screening performance of the Combined and Integrated tests (that include NT measurement) were compared using previous and revised estimates of the standard deviation.The standard deviation of NT in unaffected pregnancies has reduced over time (from 1998 to 2008) (e.g. from 0.1329 to 0.1105 [log(10) MoM] at 12-13 completed weeks of pregnancy, reducing the variance by about 30%).Compared with results from the serum, urine and ultrasound screening study (SURUSS), use of the revised NT standard deviations in unaffected pregnancies resulted in an approximate 20% decrease in the false-positive rate for a given detection rate; for example, from 2.1% to 1.7% (a 19% reduction) at a 90% detection rate using the Integrated test with first trimester markers measured at 11 completed weeks' gestation and from 4.4% to 3.5% (a 20% reduction) at an 85% detection rate using the Combined test at 11 completed weeks.

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

Objective: To determine whether the standard deviation of nuchal translucency (NT) measurements has decreased over time and if so to revise the estimate and assess the effect of revising the estimate of the standard deviation on the performance of antenatal screening for Down's syndrome.

Setting: Data from a routine antenatal screening programme for Down's syndrome comprising 106 affected and 22,640 unaffected pregnancies.

Methods: NT measurements were converted into multiple of the median (MoM) values and standard deviations of log(10) MoM values were calculated in affected and unaffected pregnancies. The screening performance of the Combined and Integrated tests (that include NT measurement) were compared using previous and revised estimates of the standard deviation.

Results: The standard deviation of NT in unaffected pregnancies has reduced over time (from 1998 to 2008) (e.g. from 0.1329 to 0.1105 [log(10) MoM] at 12-13 completed weeks of pregnancy, reducing the variance by about 30%). This was not observed in affected pregnancies. Compared with results from the serum, urine and ultrasound screening study (SURUSS), use of the revised NT standard deviations in unaffected pregnancies resulted in an approximate 20% decrease in the false-positive rate for a given detection rate; for example, from 2.1% to 1.7% (a 19% reduction) at a 90% detection rate using the Integrated test with first trimester markers measured at 11 completed weeks' gestation and from 4.4% to 3.5% (a 20% reduction) at an 85% detection rate using the Combined test at 11 completed weeks.

Conclusions: The standard deviation of NT has declined over time and using the revised estimates improves the screening performance of tests that incorporate an NT measurement.

Show MeSH
Related in: MedlinePlus