Predicting Fetal Chromosome Anomalies in the First Trimester Using Pregnancy Associated Plasma Protein-A: A Comparison of Statistical Methods

M. C. M. Macintosh; B. Brambati; T. Chard; J. G. Grudzinskas

doi:10.1055/s-0038-1634910

Methods of Information in Medicine, Inhaltsverzeichnis

Methods Inf Med 1993; 32(02): 175-179
DOI: 10.1055/s-0038-1634910

Original Article

Schattauer GmbH

Predicting Fetal Chromosome Anomalies in the First Trimester Using Pregnancy Associated Plasma Protein-A: A Comparison of Statistical Methods

M. C. M. Macintosh

¹Joint Academic Unit of Obstetrics, Gynaecology and Reproductive Physiology, St. Bartholomew’s Hospital Medical College and the London Hospital Medical College, London, UK

,

B. Brambati

²Institute of Obstetrics and Gynaecology, University of Milan, Milan, Italy

,

T. Chard

¹Joint Academic Unit of Obstetrics, Gynaecology and Reproductive Physiology, St. Bartholomew’s Hospital Medical College and the London Hospital Medical College, London, UK

,

J. G. Grudzinskas

¹Joint Academic Unit of Obstetrics, Gynaecology and Reproductive Physiology, St. Bartholomew’s Hospital Medical College and the London Hospital Medical College, London, UK

› Institutsangaben

Abstract

Abstract:

The analysis of the clinical efficiency of a biochemical parameter in the prediction of chromosome anomalies is described, using a database of 475 cases including 30 abnormalities. A comparison was made of two different approaches to the statistical analysis: the use of Gaussian frequency distributions and likelihood ratios, and logistic regression. Both methods computed that for a 5% false-positive rate approximately 60% of anomalies are detected on the basis of maternal age and serum PAPP-A. The logistic regression analysis is appropriate where the outcome variable (chromosome anomaly) is binary and the detection rates refer to the original data only. The likelihood ratio method is used to predict the outcome in the general population. The latter method depends on the data or some transformation of the data fitting a known frequency distribution (Gaussian in this case). The precision of the predicted detection rates is limited by the small sample of abnormals (30 cases). Varying the means and standard deviations (to the limits of their 95% confidence intervals) of the fitted log Gaussian distributions resulted in a detection rate varying between 42% and 79% for a 5% false-positive rate. Thus, although the likelihood ratio method is potentially the better method in determining the usefulness of a test in the general population, larger numbers of abnormal cases are required to stabilise the means and standard deviations of the fitted log Gaussian distributions.

Key-Words

First Trimester - Screening - Pregnancy-Associated Plasma Protein-A (PAPP-A) - Logistic Regression

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Referenzen

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