NUCHAL TRANSLUCENCY CANNOT BE USED AS A SCREENING-TEST FOR CHROMOSOMAL-ABNORMALITIES IN THE FIRST TRIMESTER OF PREGNANCY IN A ROUTINE ULTRASOUND PRACTICE

We decided to asses the practicability of introducing nuchal transluce ncy (NT) measurements as a screening programme for fetal Down's syndro me in the first trimester of pregnancy, within the population of women who receive ultrasound examinations in our department. Over a 1-year period, measurements were made in 923 fetuses at less than or equal to 13 weeks' gestation. Fifty-two per cent of the mothers were 36 years or older or had a past history of a chromosomally abnormal fetus or ch ild. Measurements were only successful 58 per cent of the time; this i mproved to 74 per cent if the fetus was greater than or equal to 10 we eks' gestation. Inter-observer variability did not cause a major probl em. There were 36 fetuses with an NT greater than or equal to 3 mm. Tw o of these fetuses had a chromosomal abnormality (both trisomy 21). Th e translucency in these two cases was so large that they would have be en detected and offered prenatal diagnosis even prior to this study. T here was a total of ten aneuploidies in the study group. Only two of t hese fetuses were detected by this screening method; five had an NT me asurement < 3 mm and in three fetuses (all trisomy 21), measurements w ere not successful. We outline the practical problems that could be ex pected by introducing ultrasound screening in a routine setting. Altho ugh the efficacy of the test in a research setting may seem good, the effectiveness in everyday usage appears much less impressive, making i ts uptake as a screening technique in a general ultrasound practice at this stage imprudent.