FIRST-TRIMESTER DOWNS-SYNDROME SCREENING USING NUCHAL TRANSLUCENCY - A PROSPECTIVE-STUDY IN PATIENTS UNDERGOING CHORIONIC VILLUS SAMPLING

The value of the measurement of nuchal translucency thickness for pred icting fetal Down's syndrome and other aneuploidies was prospectively evaluated at 8-15 weeks of gestation in 1819 consecutive pregnancies s cheduled for karyotyping by chorionic villus sampling. In 43 cases, a chromosomal unbalanced aberration was found. Two teams of ultrasonolog ists who examined patients attending either National Health Service (S eries I) or private practice clinics (Series 2) were involved in the s tudy. The same type of ultrasound machine and standardized approach we re used in both study groups. In those cases in which the maximum subc utaneous thickness of the translucency was 3 mm or greater, the incide nce of chromosomal aberration was 18.6% compared to 1.7% in the cases in which this was below 3 mpn. The sensitivity, specificity and relati ve risk for all aneuploidies were 30%, 96% and 10.83, respectively, an d no difference was found between trisomy 21 and other types of aneupl oidy. The sensitivity and specificity and relative risk were significa ntly higher at 9-10 weeks than between II and 15 weeks. The results we re concordant in the two series; however, the overall values for sensi tivity (20% vs. 39%), specificity (94% vs. 98%) and relative risk (4.1 3 vs. 24.20) were clearly higher in the group of private patients. The results obtained confirm the potential application of the measurement of nuchal translucency thickness for fetal aneuploidy screening befor e the end of the first trimester and suggest that a multiplicity of in dividual, structural and organizational factors may interact and play a crucial role in determining the actual efficiency of ultrasound scre ening programs.