[First trimester ultrasound screening of chromosomal abnormalities]

Abstract

Introduction: A retrocervical subcutaneous collection of fluid at 11-14 weeks of gestation, can be visualized by ultrasound as nuchal translucency (NT).

Objective: To examine the distribution of fetal nuchal translucency in low risk population, to determine the detection rate of chromosomal abnormalities in the population of interest based on maternal age and NT measurement.

Method: Screening for chromosomal defects, advocated by The Fetal Medicine Foundation (FMF), was performed in 1341 pregnancies in the period January 2000-April 2004. Initial risk for chromosomal defects (based on maternal and gestational age) and corrected risk, after the NT measurement, were calculated. Complete data were collected from 1048 patients.

Results: Out of 1048 pregnancies followed, 8 cases of Down's syndrome were observed, 7 were detected antenatally and 6 out of 7 were detected due to screening that combines maternal age and NT measurement. According to our results, sensitivity of the screening for aneuploidies based on maternal age alone was 12.5% and false positive rate 13.1%, showing that screening based on NT measurement is of great importance. Screening by a combination of maternal age and NT, and selecting a screening-positive group for invasive testing enabled detection of 75% of fetuses with trisomy 21.

Conclusion: In screening for chromosomal abnormalities, an approach which combines maternal age and NT is effective and increases the detection rate compared to the use of any single test.