Day-to-day, postprandial, and orthostatic variation of total plasma homocysteine.

However, if we obtain the same value, this does not necessarily mean that it is the most accurate one. We thank the Association pour la Recherche en Médecine Foetale for financial support and all of the manufacturers who contributed software packages. We also thank Lau-rence Bussière, who was involved in the early stages of this work. diagnosis of diverse chromosome abnormalities in a population of patients identified by triple-marker testing as screen positive for Down syndrome. AJ, et al. Second trimester maternal serum screening using alpha-fetopro-tein, human chorionic gonadotrophin, and unconjugated oestriol: experience of a regional programme. The advantages of using triple-marker screening for chromosomal abnormalities. combining maternal serum ␣-fetoprotein and hCG in a second-trimester screening program for Down syndrome. Prospective maternal serum human chorionic gonadotrophin screening for the risk of fetal chromosome anomalies and of subsequent fetal and neonatal deaths. Prospective study of prenatal screening for Down's syndrome with free ␤ human chorionic gonadotrophin. A single chorionic gonadotrophin assay for maternal serum screening for Down's syndrome. The natural history of Down syndrome conceptuses diagnosed prenatally that are not electively terminated. Rates of Down syndrome at livebirth by one-year maternal age intervals in studies with apparent close to complete ascer-tainment in populations of European origin: a proposed revised rate schedule for use in genetic and prenatal screening. Estimating a woman's risk of having a pregnancy associated with Down's syndrome using her age and serum AFP. The imprecision in rates of Down syndrome by one-year maternal age intervals: a critical analysis of rates used in biochemical screening. and neural tube defect screening: the value of using gestational age by ultrasonography. Down syndrome risks at chorionic villus sampling, amniocentesis, and livebirth in women of advanced maternal age from a uniquely defined population. Increased concentrations of the amino acid homocys-teine— hyperhomocysteinemia—are correlated with ath-erosclerotic and thrombotic diseases (1, 2). High concentrations can be lowered by diet and dietary supplements with vitamins B 12 , folate, and pyridoxine. Homocysteine is produced in the metabolism of the essential amino acid methionine and is converted by cystathionine ␤-synthase to cystathionine and by methionine synthase back to methionine. These enzymatic reactions are dependent on sufficient concentrations of the vitamins B 12 , folate, and pyridoxine. Knowledge of biological, postprandial, and orthostatic variations are important in judging significant changes in results and error sources in blood sampling conditions (3), and several studies on the biological variation of plasma …