Integrated screening for chromosomal anomalies: Strategies in developing countries

Abstract

Ultrasound screening has advantages over maternal serum screening. These include confirmation of embryo viability, accurate assessment of gestational age, early diagnosis of multiple pregnancies and identification of chorionicity, the detection of major structural abnormalities, major defects of the heart and great arteries, skeletal dysplasias and genetic syndrome and measurement of NT thickness in assessing the risk for Down's syndrome. Nuchal translucency (NT) has emerged as the most sensitive ultrasound marker for detection of chromosomal anomalies in the first trimester. However, the use of ultrasound in routine screening still faces problems with reliability and quality control. Combination of maternal age, NT and first and biochemical second-trimester markers is known as the integrated test. A major goal of screening tests is to achieve high detection rate and low false-positive rate at a low cost. The integrated test best meets these criteria. It could achieve a detection rate of 85% for a false-positive rate of 1.2%. It has a much better positive predictive value and, therefore, fewer amniocentesis and fewer losses of normal fetuses. Only screen-positive cases could be taken for invasive testing.