First Trimester Screening for Chromosomal Anomaly

Tahmaspour A.R *,


The traditional method of screening for Down’s syndrome has been maternal age where amniocentesis or chorionic villous sampling is offered to women aged 35 years or more. This results in the need for an invasive test in 15-20% of pregnant women with a detection of less than half of the fetuses with Donw’s syndrome because the majorly of affected fetuses come from the younger age group. A more effective method of screening is based in the combination of: ● Maternal age ● A maternal blood sample for the measurement of the placental products of free ß-hCG and PAPP-A ● An ultrasound scan at 11-13 weeks: ○ to measure the collection of fluid behind the fetal neck (nuchal translucency) ○ to examine the fetal nose and palate ○ to measure the fetal heart rate ○ to assess the flow of blood across the tricuspid valve of the fetal heart and the ductus venosus This new method of screening reduces dramatically the number of women requiring an invasive test from about 20% to less than 3% and at the same time increases the detection rate of Down’s syndrome and other major chromosomal abnormalities form less than 50% to more than 95%