Nuchal Translucency as a Method of First-Trimester Screening for Aneuploidy

ABSTRACT

Objective. To determine the effectiveness of nuchal translucency (NT) screening in predicting aneuploidy and structural abnormalities in a South African population. Study design. Descriptive study. Setting. Chris Hani Baragwanath Hospital fetal medicine unit. Outcome measures. An adjusted risk was derived from the combination of maternal age-related risk and the risk derived from NT screening. A positive screen was denoted by an adjusted risk of more than 1/300 and a negative screen by an adjusted risk of less than 1/300. In order to determine the number of undiagnosed abnormalities in the group; all babies were examined by a paediatrician at birth to detect and describe dysmorphic features. Results. A total of 428 patients underwent first-trimester screening between July 2003 and July 2005. Three per cent were lost to follow-up. Of the 415 patients analysed; 59 screened positive and 356 screened negative. The mean age for both groups of patients was 30.1 years. Of the 57 patients who screened positive; 24 elected to have chorionic villus sampling (CVS). This resulted in the detection of 6 chromosomal abnormalities and 2 structural abnormalities. Among the remaining 356 patients; who had screened negative; 2 had an increase in the adjusted risk when the risk was compared with the background risk; and 1 chromosomal abnormality was detected in this group; 8 elected to have CVS because of a previous history of a chromosomal abnormality; and there were no abnormalities among them. Conclusions. The use of these screening methods has enabled prenatal karyotyping to become cost effective; and allows concentration on pregnancies at highest risk for chromosomal abnormalities; regardless of age