The purpose of this scan is to:
✓ Demonstrate that the fetus is alive.
✓ Date the pregnancy from the measurement of the size of the fetus.
✓ Diagnose or exclude some major fetal abnormalities (upto 75% of anomalies can be excluded at this stage).
✓ Diagnose multiple pregnancies and determine the chorionicity (to decide whether identical or non-identical foetuses and this crucial for the management)
Measure the nuchal translucency (fluid behind the fetal neck), to look for fetal nasal bone and in few high risk cases to study the blood flow through the heart valve (to look for tricuspid regurgitation) and flow in ductus venosus (in fetal liver).The scan done by a specialist who is certified from the fetal medicine foundation UK.These are used for calculating the chance that the fetus has Down’s syndrome and other major chromosomal abnormalities. Combining the ultrasound findings with measurement of two hormones produced by the placenta (by doing blood test from the mother) will achieve close to 95% detection rate (with 2.5% false positive rate) of Down’s syndrome. Basic details about pregnancy such as last menstrual period,mother’s age,weight,and medical/obstetric history also need to be included for the risk calculation.