Nuchal translucency as a method of first trimester screening for aneuploidy in a South African population

摘要

ABSTRACTudNuchal Translucency as a method of First Trimester Screening for Aneuploidy in audSouth African populationudBackgroundudChromosomal abnormalities constitute 15% of congenital abnormalities and 50% ofudpregnancy losses. Twenty-five percent of these will be Trisomy 21. Down’s syndrome has audbirth incidence of 2 per 1000 and constitutes 25% of severe mental handicap in the developedudworld. Whereas the risk assessment focuses on Trisomy 21, the fetuses that screen positive areudalso known to contain other defects, which include anomalies such as cardiac defects,uddiaphragmatic hernias, neuromuscular disorders, and rare genetic syndromes.udObjectiveudTo determine the effectiveness of nuchal translucency (NT) screening in predicting aneuploidyudand structural abnormalities in a South African populationudSettingudChris Hani Baragwanath Hospital Fetal Medicine UnitudStudy designudDescriptive StudyudMethodologyudThe Fetal Medicine Unit database was reviewed and the records of patients who hadudundergone NT screening between July 2003 and July 2005 were retrieved. There were noudexclusions. An adjusted risk was derived from the combination of age-related risk and the riskudderived from nuchal translucency screening. A positive screen was denoted by an adjusted riskudof more than 1/300 and a negative screen was denoted by an adjusted risk of less than 1/300.udResultsudA total of 428 patients had first trimester screening during this period. Thirteen patients (3%)udwere lost to follow up. Of the 415 cases that were analyzed, 57 patients screened positive andud356 patients screened negative. In addition, 2 fetuses with acrania were detected. The meanudage for both groups of patients was 30.1 years. The crown-rump length of fetuses with audpositive screen was statistically significantly shorter than fetuses that screened negative. Ofudthe 57 patients that screened positive 24 elected to have chorionic villus sampling (CVS)udwhich resulted in the detection of 6 chromosomal abnormalities and 2 structural abnormalities.udOf the remaining 356 patients, who had screened negative, 2 had an increased adjusted risk,udand one chromosomal abnormality was detected in this group.udOf the remaining 354 patients, 8 elected to have CVS because of a previous history ofudchromosomal abnormality. All of them proved to be normal.udConclusionsudThe use of such screening has enabled prenatal karyotyping to be focused on pregnancies atudhighest risk for chromosomal abnormalities regardless of age.